Pressure-sensitive adhesive sheet

ABSTRACT

Provided is a PSA sheet with which good air release properties can be obtained while whose quality can be further enhanced. This invention provides a PSA sheet comprising a substrate film and a PSA layer provided to at least one face of the substrate film. The PSA sheet further comprises a coating layer partially covering the PSA layer surface. The PSA sheet&#39;s adhesive is formed of the PSA layer and the coating layer. The coating layer has a linearly extending part running from one edge to another edge of the adhesive face. The linearly extending part has a first face forming the PSA sheet&#39;s adhesive face and a second face located on the PSA layer side relative to the first face. The second face of the linearly extending part forms an overall gently curved line in a cross section perpendicularly intersecting the length direction of the linearly extending part.

TECHNICAL FIELD

The present invention relates to a pressure-sensitive adhesive sheet.

This application claims priority to Japanese Patent Application No.2014-242183 filed on Nov. 28, 2014 and Japanese Patent Application No.2015-164269 filed on Aug. 21, 2015; the entire contents thereof areincorporated herein by reference.

BACKGROUND ART

In general, pressure-sensitive adhesive (or PSA; the same applieshereinafter) has characteristics to be in a soft solid (viscoelastic)state in a room temperature range and easily adhere to adherend withsome pressure. With the benefit of such properties, PSA is widely usedin forms of substrate-supported PSA sheets having a PSA layer at leaston one face of the substrate for purposes including fastening andsurface protection of various articles and obtaining desirableappearances such as for decorative purposes. Documents disclosing thesetypes of conventional art include Patent Documents 1 and 2.

CITATION LIST Patent Literature

-   [Patent Document 1] Japanese Patent Application Publication No.    2006-70273-   [Patent Document 2] Japanese Patent Application Publication No.    2000-160117

SUMMARY OF INVENTION Technical Problem

With respect to conventional PSA sheets, when the PSA sheets are adheredto adherends, there have been cases where a fluid substance such as airis left between the PSA sheets and the adherends to form bubbles and thelike (trapped air, etc.), thereby causing degradation of theappearances. Such bubbles and the like are not desirable, either, inview of their negative impact on the adhesive properties such as reducedadhesive strength. To prevent formation of the bubbles and the like orto provide features (or air release properties) to eliminate the sort ofbubbles if formed, there is a known technique by which ridges are formedon the surface of a release liner that protects the adhesive face of aPSA sheet and the ridges are used to form grooves in the PSA layersurface (Patent Document 1). Air and the like that are to remain betweenthe adhesive face and the adherend can be eliminated through the groovesformed in the surface of the PSA layer. Methods by which grooves areformed in the PSA layer surface as described in Patent Document 1 have aproblem that depending on the thickness of the PSA layer, the depth ofthe grooves serving as pathways for air and the like is limited; andafter removal of the release liner and the like to expose the adhesiveface, if it takes time before its application to an adherend, theviscoelasticity of the PSA layer causes the grooves to fade or be lost,whereby no air release properties are obtained. In addition, when thePSA sheet is peeled off the adherend, there may be a tendency for theoccurrence of leftover adhesive residue with the grooves serving asinitiation points. Patent Document 2 discloses partial lamination of anon-adhesive layer on the PSA layer surface and the use of thenon-adhesive layer surface as a passageway for air and the like toensure air release properties. However, it does not examine the state ofcontact between the non-adhesive layer and the PSA layer or how thestate of contact would affect the quality of the PSA sheet.

The present inventors examined how the quality can be improved for a PSAsheet that comprises a coating layer partially covering a PSA layersurface and have completed the present invention with focus on thecoating layer's shape (cross-sectional shape) in the depth direction.The present invention is thus related to improvement of a PSA sheet thathas a coating layer as an air releasing means placed partially on thePSA layer surface, with an objective to provide a PSA sheet thatcomprises a coating layer having a novel cross-sectional shape likely tofit with PSA whereby good air release properties are obtained and thequality can be further enhanced.

Solution to Problem

The present invention provides a PSA sheet comprising a substrate filmand a PSA layer provided to at least one face of the substrate film. ThePSA sheet further comprises a coating layer that partially covers thesurface of the PSA layer. The adhesive face of the PSA sheet is formedof the PSA layer and the coating layer. The coating layer has a linearlyextending part that runs from one edge to another edge of the adhesiveface. The linearly extending part has a first face forming the adhesiveface of the PSA sheet and a second face located on the PSA layer siderelative to the first face. The second face of the linearly extendingpart forms an overall gently curved line in a cross section thatperpendicularly intersects the length direction of the linearlyextending part.

The viscoelastic material forming the PSA layer is likely to fit withthe coating layer having such a cross-sectional shape. Even with respectto coating layers having the same surface pattern and the samethickness, when the coating layer has a cross-sectional shape asdescribed above, the surface condition of the PSA layer and thetightness of adhesion between the PSA layer and the coating layer can besuperior as compared to when the coating layer does not have such across-sectional shape. According to this embodiment, in the PSA sheetcomprising the coating layer that partially covers the PSA layersurface, good air release properties are obtained while the quality canbe further enhanced. While no particular limitations are to be imposed,the effects of this invention are obtained through the novelcross-sectional shape of the coating layer. Thus, the PSA components andthe coating layer material are not limited. This may be effective inremoving limitations to the materials used such as the use of arelatively hard material as the PSA to maintain the groove shape inPatent Document 1.

Herein, “forming an overall gently curved line” means that it draws anoverall gently curved line which may partially include a straight line(e.g. at the bottom of the coating layer, etc.). It also means beingentirely free of corners when observed at 10000× magnification (inparticular, when observing an SEM (scanning electron microscopy) or TEM(transmission electron microscopy) cross-sectional image of a linearlyextending part of the coating layer at 10000× magnification). In otherwords, it means being free of corners at the submicroscopic (0.1 μm)level and preferably being free of inflection points.

In a preferable embodiment of the PSA sheet disclosed herein, in thecross section that perpendicularly intersects the length direction ofthe linearly extending part, the second face of the linearly extendingpart has a segment that starts from one edge of the linearly extendingpart and runs towards the middle in a gently curved line in the depthdirection of the PSA layer. The one edge is typically each edge. Inother words, the segment that runs in a gently curved line in the depthdirection of the PSA layer refers to one edge portion or each of the twoend portions (each of the two ends). When the edges of the widthdirection of the linearly extending part are in such an embodiment, thePSA fits well with the coating layer. The edge portions can basicallyform the adhesive face of the PSA sheet, high quality of the edgeportions leads to high quality of the adhesive face.

Herein, that it “starts from one edge of a linearly extending part andruns towards the middle in a gently curved line while sinking in thedepth direction of the PSA layer” is not limited to a specific slope orcurved shape. In typical, the concept includes having a gentle slopesuch that it always satisfies that, in a cross section perpendicularlyintersecting the length direction of a linearly extending part, on theline of the second face of the linearly extending part, at X μm towardsthe middle from one edge of the linearly extending part, the second facehas a depth less than 1/√2X μm (preferably less than 1/√3X μm, morepreferably less than ½X μm, e.g. less than ⅓X μm). The depth of thesecond face of the linearly extending part refers to the depth of thesecond face relative to the outer surface of the PSA layer (precisely,relative to the imaginary flat surface formed with the outer surface ofthe PSA layer). X is a positive integer and its upper limit is a halfthe width of the linearly extending part. For instance, when a linearlyextending part of the coating layer has a thickness less than 3 μm, at Xin a range of 10 μm or less (more restrictedly in a range of 5 μm orless), on the line formed by the second face of the linearly extendingpart, at X μm towards the middle from one edge of the linearly extendingpart, it is preferable that the second face always has a depth less than1/√3X μm (preferably less than ½X μm, more preferably less than ⅓X μm,e.g. less than ¼X μm).

In a preferable embodiment of the PSA sheet disclosed herein, in thecross section that perpendicularly intersects the length direction ofthe linearly extending part, the second face of the linearly extendingpart has an inclined segment that runs from one edge of the linearlyextending part in the depth direction of the PSA layer and a flatsegment that includes the deepest point of the linearly extending partand runs mostly parallel to the adhesive face. With the inclusion of theinclined segment, the effects of this invention are preferably realized.It is noted that the one edge is typically each edge; and in this case,the inclined segment is present at each end of the width direction ofthe linearly extending part.

In a preferable embodiment of the PSA sheet disclosed herein, theinclined segment is curved, convex on the PSA layer side. Such anembodiment preferably brings about the effects of this invention.

In a preferable embodiment of the PSA sheet disclosed herein, thelinearly extending part has a thickness T and a width W with a W/T ratioof 50 or higher. With respect to such an embodiment, the effects of thisinvention are more preferably produced.

In a preferable embodiment of the PSA sheet disclosed herein, thelinearly extending part has a width of 100 μm or greater. With respectto such an embodiment, the effects of this invention are more preferablyproduced.

The present invention also provides a release liner-backed PSA sheetcomprising a PSA sheet disclosed herein and a release liner thatprotects an adhesive face of the PSA sheet. Of the surfaces of therelease liner, the adhesive face-side surface is preferably formedsmooth. In such an embodiment, greater adhesive properties tend to beobtained. According to the art disclosed herein, in this embodiment,when the release liner is used as a coating layer-transferring film, agood transfer of the coating layer can be obtained.

The present invention also provides a release liner for PSA sheets, therelease liner comprising a releasable support having at least onereleasable face. The releasable face of the releasable support isprovided with a coating layer that can be transferred onto a PSA sheet.The coating layer has a linearly extending part that runs from one edgeto another edge of the releasable face. The linearly extending part hasa first face located on the releasable face side and a second faceforming the outer surface on the releasable face. The second face of thelinearly extending part forms an overall gently curved line in a crosssection that perpendicularly intersects the length direction of thelinearly extending part. With the use of such a release liner totransfer the coating layer onto the PSA layer surface of the PSA sheet,a high-quality PSA sheet having good air release properties can be made.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic top view of the PSA sheet according to anembodiment.

FIG. 2 shows a cross-sectional diagram at line II-II in FIG. 1.

FIG. 3 shows a cross section of a linearly extending part(perpendicularly intersecting the length direction) of the coating layeraccording to an embodiment in an enlarged schematic cross-sectionalview.

FIG. 4 shows the left edge of the coating layer in FIG. 3 in a furtherenlarged schematic cross-sectional view.

FIG. 5 shows the right edge of the coating layer in FIG. 3 in a furtherenlarged schematic cross-sectional view.

FIG. 6 shows a schematic cross-sectional diagram of the releaseliner-backed PSA sheet according to an embodiment.

FIG. 7 shows a schematic cross-sectional diagram of the releaseliner-backed PSA sheet according to another embodiment.

FIG. 8 shows a schematic cross-sectional diagram of the release linerfor the PSA sheet according to an embodiment.

FIG. 9 shows an SEM cross-sectional image of the PSA sheet of a workingexample.

FIG. 10 shows an SEM cross-sectional image of the PSA sheet of theworking example, showing one edge (left edge) of the coating layer inFIG. 9 in an enlarged view.

FIG. 11 shows an SEM cross-sectional image of the PSA sheet of theworking example, showing a flat segment at the center of the coatinglayer in FIG. 9 in an enlarged view.

FIG. 12 shows an SEM cross-sectional image of the PSA sheet of theworking example, showing the other edge (right edge) of the coatinglayer in FIG. 9 in an enlarged view.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention are described below.Matters necessary to practice this invention other than thosespecifically referred to in this description may be comprehended by aperson of ordinary skill in the art based on the instruction regardingimplementations of the invention according to this description and thecommon technical knowledge in the pertinent field. The present inventioncan be practiced based on the contents disclosed in this description andcommon technical knowledge in the subject field. In the drawingsreferenced below, a common reference numeral may be assigned to membersor sites producing the same effects, and duplicated descriptions aresometimes omitted or simplified. The embodiments described in thedrawings are schematized for clear illustration of the presentinvention, and do not necessarily represent the accurate sizes orreduction scales of the PSA sheet of the present invention provided asan actual product.

The concept of PSA sheet herein encompasses so-called PSA tapes, PSAlabels, and PSA films. The PSA sheet disclosed herein can be in a rollform or in a flat sheet form. Alternatively, the sheet may be furtherprocessed into various forms.

FIG. 1 shows a schematic top view of the PSA sheet according to anembodiment. FIG. 2 shows a cross-sectional diagram at line II-II inFIG. 1. With reference to the drawings, the PSA sheet in this embodimentis described.

As shown in FIGS. 1 and 2, PSA sheet 1 according to this embodiment hasa layered structure formed of a substrate film 10 and a PSA layer 20.Substrate film 10 supports the PSA layer 20. In PSA sheet 1, the surface20A on the PSA layer 20 side forms an adhesive face 1A. The other face1B (the surface on the film substrate 10 side) of PSA sheet 1 is anon-adhesive face.

On the surface 20A of the PSA layer 20, a coating layer 30 is partiallyplaced. In other words, the PSA layer surface 20A is partially coveredwith the coating layer 30. When PSA sheet 1 is applied to an adherend,the coating layer 30 forms pathways for air and the like between the PSAsheet 1 and the adherend, whereby air release properties are provided.

The coating layer 30 has a prescribed pattern (coating layer pattern) 40on the adhesive face 1A of the PSA sheet 1. In this embodiment, thecoating layer 30 is in a lattice pattern 40. In particular, the latticepattern 40 of the coating layer 30 is formed of the first stripe pattern42 and the second stripe pattern 44 that is placed to intersect thefirst stripe pattern 42.

The first stripe pattern 42 is formed of parts 50 (linearly extendingparts, bands in this embodiment) that run straight from one edge toanother edge of the adhesive face 1A. These linearly extending parts 50are placed in parallel, spaced at intervals arranged in the widthdirection. In this embodiment, the linearly extending parts 50 areplaced at an angle such that their length directions intersect the edges(ends, limits) of the width direction of PSA sheet 1, with each partreaching two edges (two sides) of the adhesive face 1A.

Similarly to the first stripe pattern 42, the second stripe pattern 44is also formed of parts 50 (linearly extending parts, bands in thisembodiment) that run straight from one edge to another edge of theadhesive face 1A. These linearly extending parts 50 are placed inparallel at intervals arranged in the width direction. In thisembodiment, the linearly extending parts 50 are placed at an angle suchthat their length directions intersect the edges of the width directionof PSA sheet 1, with each part reaching two edges (two sides) of theadhesive face 1A. In this embodiment, the linearly extending parts 50are straight bands, but are not limited thereto. Each linearly extendingpart may be curvilinear. In such an embodiment, the several linearlyextending parts may form a wavy stripe pattern, etc. The number of thelinearly extending parts (the number of lines) may depend on the shape,size, etc., of the adhesive face of the PSA sheet; and therefore, it isnot limited to a particular number.

In this embodiment, the first stripe pattern 42 and the second stripepattern 44 intersect each other so that the linearly extending parts 50of the first stripe pattern 42 and the linearly extending parts 50 ofthe second stripe pattern 44 cross one another almost perpendicularly.Thus, the linearly extending parts 50 of the first stripe pattern 42partially overlap the linearly extending parts 50 of the second stripepattern 44.

Herein, the lattice pattern typically refers to a pattern that includestwo stripe patterns intersecting each other and encompasses not only arhombic lattice as in the present embodiment, but also various latticeshapes such as a square lattice and a triangular lattice. When thelinearly extending parts are straight, the angle (the acute angle) at anintersection of the two stripe patterns can be in a range from 10° to90° (preferably 45° to 90°, typically 60° to 90°). The lattice patterndisclosed herein also encompasses a pattern that includes a stripepattern formed of several linearly extending parts with repeatedbending, for instance, a pattern such as a hexagonal lattice. In such apattern, adjacent linearly extending parts may be partially connected toone another. From the standpoint of the air release properties, thecoating layer preferably comprises one, two or more stripe patterns. Thecoating layer pattern (typically a lattice pattern) may include a thirdstripe pattern.

Described next is a cross-sectional shape of the coating layer 30. FIG.3 shows a cross section of a linearly extending part (the cross sectionperpendicularly intersecting the length direction) of the coating layeraccording to an embodiment in an enlarged schematic cross-sectionalview. FIG. 4 shows the left edge of the coating layer in FIG. 3 in afurther enlarged schematic cross-sectional view. FIG. 5 shows the rightedge of the coating layer in FIG. 3 in a further enlarged schematiccross-sectional view.

As shown in FIG. 3, a linearly extending part 50 of the coating layer 30is in a thin layer laminated partially on the surface 20A of the PSAlayer 20 and has a first face 52 that forms the adhesive face 1A of thePSA sheet 1 and a second face 54 located on the PSA layer 20 siderelative to the first face 52. In particular, the surfaces of thelinearly extending part 50 are formed with the first face (outersurface) 52 and the second face (inner surface) 54 as the back face ofthe first face 52.

The first face 52 of the linearly extending part 50 is flush with orprotrudes slightly from the outer surface of the PSA layer 20. From thestandpoint of the air release properties, it is preferable that thefirst face 52 of the linearly extending part 50 protrudes slightly fromthe outer surface of the PSA layer 20. The height of the protrudingportion of the first face of the linearly extending part (the heightrelative to the outer surface of the PSA layer (precisely, relative tothe imaginary flat surface formed with the outer surface of the PSAlayer)) is preferably less than 30% (e.g. less than 10%) of thethickness of the linearly extending part. It is noted that the thicknessof the linearly extending part is basically identical to the thicknessof the coating layer.

The second face 54 of the linearly extending part 50 forms an overallgently curved line in a cross section that perpendicularly intersectsthe length direction of the linearly extending part 50. In particular,as shown in FIG. 4, in the cross section, the second face 54 of alinearly extending part 50 has a segment that starts from one edge 56(the left edge in the drawing) of the linearly extending part 50 andruns towards the middle in a gently curved line while sinking in thedepth direction (the thickness direction) of the PSA layer 20.Similarly, as shown in FIG. 5, the second face 54 of a linearlyextending part 50 has a segment that starts from the other edge 58 (theright edge in the drawing) of the linearly extending part 50 and runstowards the middle in a gently curved line while sinking in the depthdirection (the thickness direction) of the PSA layer 20. The one edge 56and the other edge 58 correspond to the two edges of the width directionof the linearly extending part 50.

More specifically, the second face 54 of a linearly extending part 50has an inclined segment 60 and a flat segment 62 that continues from theinclined segment 60. In the cross section, the inclined segment 60 has ashape that runs from the one edge 56 of the linearly extending part 50in the depth direction of the PSA layer 20. The flat segment 62 of thesecond face 54 is a range that includes the deepest portion of thelinearly extending part 50. In this embodiment, in the cross section, itruns mostly parallel to the adhesive face 1A of the PSA sheet 1.

In this embodiment, the inclined segment 60 is formed in an area runningfrom the one edge 56 of the width direction of the linearly extendingpart 50 to about 10 μm towards the middle in the width direction, and anarea running from the other edge 58 of the width direction of thelinearly extending part 50 to about 10 μm towards the middle in thewidth direction. The rest of the second face 54 (i.e. the bottom of thecoating layer 30) forms the flat segment 62. The inclined segment 60 iscurved, convex on the PSA layer 20 side.

The range to which the inclined segment is formed is not limited tothose described above. When a linearly extending part of the coatinglayer has a maximum depth of D μm, the inclined segment can be formed ina range that runs from one of the two edges of the width direction ofthe linearly extending part to 10·D μm (typically 7·D μm, e.g. 4·D μm)towards the middle in the width direction. For instance, when thelinearly extending part of the coating layer has a maximum depth in arange of 0.5 μm to 2 μm, the inclined segment may be formed in a rangethat runs from one of the two edges of the width direction of thelinearly extending part up to 20 μm (typically 14 μm, e.g. 8.0 μm) or upto 5.0 μm (typically 3.5 μm, e.g. 2.0 μm) towards the middle in thewidth direction. The depth of the linearly extending part is the depthof the second face of the linearly extending part, referring to thedepth of the linearly extending part relative to the outer surface ofthe PSA layer (precisely, relative to the imaginary flat surface formedwith the outer surface of the PSA layer). The same is true with themaximum depth (the depth of the deepest point).

From the one edge 56 or the other edge 58 of the width direction of thelinearly extending part 50 up to at least about 1 μm (e.g. 2 μm,typically 3 μm) towards the middle in the width direction, the inclinedsegment 60 has a slope that can be confirmed in a cross-sectional image(e.g. an SEM cross-sectional image) at 10000× magnification(specifically, a slope that has, in the cross section, an angle of, forinstance, 5° or greater, typically 10° or greater between the adhesiveface 1A and the inclined segment 60). The slope of the inclined segment60 is suitably in a range such that the angle between the adhesive face1A and the inclined segment 60 in the cross section is about 60° or less(e.g. 45° or less, typically 30° or less).

In this embodiment, the maximum depth of the linearly extending parts 50of the coating layer 30 is about 1.5 μm, but the maximum depth is notlimited to this. The maximum depth of the linearly extending parts ofthe coating layer is preferably up to about a half (e.g. up toone-third, typically up to one-fifth) the thickness of the PSA layer. Inparticular, from the standpoint of the air release properties, themaximum depth of the linearly extending parts of the coating layer ispreferably 0.1 μm or greater (e.g. 0.5 μm or greater, typically 1 μm orgreater). The maximum depth is preferably 10 μm or less, or morepreferably 5 μm or less (e.g. 3 μm or less, typically 2 μm or less).When the first face of the coating layer is almost flush with the outersurface of the PSA layer, the maximum depth of the linearly extendingparts of the coating layer is about the same as the thickness of thecoating layer. The maximum depth of a linearly extending part of thecoating layer can be obtained by SEM or TEM analysis.

The width (W1) of each linearly extending part 50 of the coating layer30 is about 200 μm in the present embodiment, but is not limited tothis. In a preferable embodiment, the width (W1) of each linearlyextending part of the coating layer is in a range of 0.1 mm to 2 mm.This can combine high long-term adhesive strength (adhesive strengthafter aged) and good air release properties. From the standpoint ofenhancing the air release properties, the width (W1) of the linearlyextending part is more preferably 0.2 mm or greater, yet more preferably0.3 mm or greater, or particularly preferably 0.5 mm or greater. Inanother preferable embodiment, the width (W1) of each linearly extendingpart of the coating layer is about 10 μm or greater. From the standpointof the air release properties, the width (W1) of each linearly extendingpart of the coating layer is preferably 50 μm or greater, morepreferably 100 μm or greater, or yet more preferably 150 μm or greater.From the standpoint of the adhesive strength, the appearance, etc., thewidth (W1) of the linearly extending part is more preferably 12 mm orless, yet more preferably 1.0 mm or less, even more preferably 0.7 mm orless, particularly preferably 0.5 mm or less, or most preferably 0.4 mmor less. The width (W1) of a linearly extending part of the first stripepattern can be equal to or different from the width (W1) of a linearlyextending part of the second stripe pattern.

In a preferable embodiment, from the standpoint of the air releaseproperties, a linearly extending part has a ratio (W/T) of its width Wto its thickness T of about 50 or higher. The ratio (W/T) is morepreferably about 80 or higher, or yet more preferably 100 or higher(typically 120 or higher). From the standpoint of the balance betweenair release properties and adhesion, the ratio (W/T) is preferably about500 or lower (e.g. 200 or lower, typically 165 or lower).

The intervals (W2) between the linearly extending parts 50 forming thefirst stripe pattern 42 of the coating layer 30 are about 18 mm in thisembodiment and the same applies to the intervals (W2) between thelinearly extending parts 50 forming the second stripe pattern 44, butneither is limited to this. The intervals (W2) between the linearlyextending parts forming the first stripe pattern are preferably in arange of 1.0 mm to 10 mm. By this, there is a higher tendency that highlong-term adhesive strength is combined with air release properties in awell-balanced manner. Here, the intervals (W2) between the linearlyextending parts refer to the widths of spaces present between any twoadjacent linearly extending parts in the adhesive face of the PSA sheet.From the standpoint of increasing the long-term adhesive strength, etc.,the intervals (W2) between the linearly extending parts are morepreferably 1.5 mm or greater, or yet more preferably 2.5 mm or greater.The intervals (W2) between the linearly extending parts can be about 8mm or less (e.g. 5 mm or less, typically 3 mm or less). The intervals(W2) between the linearly extending parts forming the second stripepattern can also be preferably selected from the ranges exemplified forthe intervals (W2) between the linearly extending parts forming thefirst stripe pattern. The intervals (W2) are preferably evenly spaced.The intervals (W2) between the linearly extending parts forming thefirst stripe pattern can be equal to or different from the intervals(W2) between the linearly extending parts forming the second stripepattern.

From the standpoint of combining well-balanced high long-term adhesivestrength and air release properties, the pitch the linearly extendingparts is preferably in a range of 1 mm to 20 mm. The pitch of thelinearly extending parts is more preferably 1.5 mm or greater, yet morepreferably 2 mm or greater (e g 2.5 mm or greater); it is morepreferably 15 mm or less (e.g. 12 mm or less), or yet more preferably 5mm or less. The pitch refers to the distance (interval) between thecenterlines of the width directions (i.e. the lengthwise centerlines) ofthe linearly extending parts.

With focus on the surface 20A of the PSA layer 20, the embodiment abovecan be described such that the surface 20A of the PSA layer 20 has acoating layer-bearing area 70 where the coating layer 30 is placed and acoating layer-free area 72 where the PSA layer 20 is exposed on theouter surface without the coating layer 30. The features (shape,arrangement, relative position, size, etc.) of the coating layer-bearingarea 70 in the PSA layer surface 20A are the same with the features ofthe coating layer 30 in the adhesive face 1A of the PSA sheet 1. Thus,the coating layer-bearing area 70 is in a pattern (a lattice pattern)that has the same features as the coating layer pattern 40 with a firststripe pattern having the same features as the first stripe pattern 42and a second stripe pattern having the same features as the secondstripe pattern 44. The first stripe pattern of the coating layer-bearingarea 70 has linearly extending parts that have the same features as thelinearly extending parts 50 that the first stripe pattern 42 has. Thesecond stripe pattern of the coating layer-bearing area 70 has linearlyextending parts that have the same features as the linearly extendingparts 50 that the second stripe pattern 44 has. Thus, details of thefeatures of the coating layer-bearing area 70 and the coating layer-freearea 72 are omitted here.

Before used, as shown in FIG. 6, the PSA sheet 1 may be in a form of arelease liner-backed PSA sheet 1 protected with a release liner 100having a release face on the adhesive face 1A side. Alternatively, itmay be in a form such that the back face (opposite from the PSA layer 20side surface) of substrate film 10 is a release face and the PSA sheet 1is wound so that the back face is brought into contact with the PSAlayer 20 whereby the PSA layer 20 is protected with the back face of thesubstrate film. Such an adhesively single-faced PSA sheet (single-facedPSA sheet) having only one adhesive face is favorable, for instance,when the surface opposite from the adhesive face requires features suchas decoration and surface protection, or when it is used as a paintsubstitute sheet.

When the PSA sheet disclosed herein is an adhesively double-facedsubstrate-backed PSA sheet (a double-faced PSA sheet) as shown in FIG.7, the PSA sheet 2 may be in an embodiment such that the respectivefaces (both non-releasable) of substrate film 10 are provided with PSAlayers 21 and 22 with the PSA layers 21 and 22 protected with releaseliners 101 and 102, respectively, with each liner having a release faceat least on the PSA layer side. In the PSA sheet 2, a coating layer 30is partially placed only on the surface of the PSA layer 21, and nocoating layer is formed on the PSA layer 22. Alternatively, although notspecifically shown in a drawing, the double-faced PSA sheet may be in anembodiment such that PSA layers are provided to the respective faces(both non-releasable) of the substrate film and one of the PSA layers isprotected with a release liner having a release face on each side. Bywinding the PSA sheet so that the other PSA layer is brought intocontact with the back face of the release liner, this type of PSA sheetcan be made into an embodiment where the two PSA layers are protectedwith the one release liner. The double-faced PSA sheet is preferablyused, for instance, for bonding/fixing applications.

<Properties of PSA Sheet, Etc.>

In the PSA sheet disclosed herein, the % surface area of the coatinglayer-free area in the PSA layer surface (which can be the % surfacearea of the coating layer in the adhesive face of the PSA sheet) ispreferably 70% or higher. This can ensure high long-term adhesivestrength. The % surface area is more preferably 75% or higher, or yetmore preferably 80% or higher; from the standpoint of obtaining good airrelease properties, the % surface area is preferably 90% or lower, ormore preferably 85% or lower.

In a preferable embodiment, the adhesive face (typically formed of theouter surface of the PSA layer and the coating layer surface) of the PSAsheet shows a 24-hour 180° adhesive strength (180° adhesive strengthafter 24-hour adhesion, or a 24-hour adhesion strength, hereinafter) of13 N/25 mm or greater. The PSA sheet can exhibit at least a certainlevel of long-term adhesive strength (adhesive strength after aged)while having good air release properties. The 24-hour adhesion strengthis preferably 14 N/25 mm or greater (e.g. 16 N/25 mm or greater). Inanother preferable embodiment, the adhesive face of the PSA sheet showsa 24-hour adhesion strength of 2 N/20 mm or greater (preferably 5 N/20mm or greater, or more preferably 8 N/20 mm or greater). The 24-houradhesion strength can be determined by the method described next. Inparticular, the PSA sheet is cut to a 20 mm or 25 mm wide by 100 mm longsize to obtain a measurement sample; and in an environment at 23° C. and50% RH, the adhesive face of the measurement sample is press-bonded tothe surface of a stainless steel plate (SUS 304BA plate) with a 2 kgroller moved back and forth once. This is left standing in the sameenvironment for 24 hours. Subsequently, using a universaltensile/compression tester, based on JIS Z 0237:2000, the peel strength(N/20 mm or N/25 mm) is determined at a tensile speed of 300 mm/min at apeel angle of 180°.

In a preferable embodiment, the PSA sheet has transparency (includingsemi-transparency). In such a PSA sheet, when bubbles and the like aretrapped between the PSA sheet and an adherend, they are visible throughthe PSA sheet and are likely to degrade the appearance. The artdisclosed herein prevents formation of the sort of bubbles between thePSA sheet and the adherend; and therefore, an excellent appearance canbe obtained in a transparent PSA sheet. That the PSA sheet istransparent means that the components (PSA layer, substrate film andcoating layer) of the PSA sheet are transparent. Herein, that the PSAsheet and its components (PSA layer, substrate film and coating layer)are transparent may mean that the PSA sheet and its components show atotal light transmittance of 80% or higher (e.g. 90% or higher,typically 95% or higher). The PSA sheet preferably has a haze value of10% or lower (e.g. 5% or lower). The total light transmittance and thehaze value can be determined using a commercial transmissometer (e.g.product name HAZE METER HM-150 available from Murakami Color ResearchLaboratory). The total light transmittance and the haze value of thesubstrate film described later are also determined by the same methods.

The overall thickness of the PSA sheet disclosed herein (including thePSA layer and the substrate, but excluding the release liner) is notparticularly limited. It is suitably in a range of about 2 μm to 1000μm, or preferably 5 μm to 500 μm (e.g. 10 μm to 300 μm, typically 30 μmto 100 μm). In a preferable embodiment, the PSA sheet has an overallthickness of 50 μm or less, or more preferably 30 μm or less (e.g. 15 μmor less, typically 5 μm or less). According to the art disclosed herein,good air release properties can be obtained even when the PSA sheet islimited in overall thickness as described above. The PSA sheet limitedin overall thickness can be advantageous in view of making products towhich the PSA sheet is applied smaller, lighter, resource-saving, and soon.

The tolerance for thickness of the PSA sheet disclosed herein ispreferably 50% or less. The PSA sheet with a small tolerance forthickness can exhibit greater adhesive properties. The tolerance forthickness is more preferably 40% or less, yet more preferably 30% orless, or particularly preferably 20% or less. The tolerance forthickness of the PSA sheet is determined by the method described laterin Examples.

<Substrate Film>

Examples of the substrate film disclosed herein include resin film,paper, cloth, rubber film, foam film, and metal foil as well as acomposite and a laminate of these. In particular, from the standpoint ofthe ease of application and the appearance, it preferably comprises aresin film layer. The inclusion of the resin film layer is advantageousalso from the standpoint of the size stability, the accuracy ofthickness, the ease of processing, the tensile strength and so on.Examples of the resin film include polyolefinic resin film such aspolyethylene (PE), polypropylene (PP), and ethylene/polypropylenecopolymers; polyester-based resin film such as polyethyleneterephthalate (PET), polybutylene terephthalate, and polyethylenenaphthalate; vinyl chloride-based resin film; vinyl acetate-based resinfilm; polyimide-based resin film; polyamide-based resin film;fluororesin film; and cellophane. Favorable examples include resin filmsformed from PE, PP and PET. Among the resin films, polyester film ismore preferable; among them, PET film is even more preferable. Thesubstrate film may have a monolayer structure or a multilayer structureformed of two, three or more layers.

In a preferable embodiment, the substrate film is a substrate comprisinga foam film (a foam-containing substrate). This providesimpact-absorbing capabilities to the PSA sheet. Here, the foam filmrefers to a film structure having a part with foam cells (a foam cellstructure). The foam-containing substrate may be a mono-layer structureformed from a foam film or a multi-layer structure wherein at least oneof whose two or more layers is formed of a foam film (a foam layer). Aconfigurational example of the foam-containing substrate is a compositesubstrate in which a foam film (a foam layer) and a non-foamed film (anon-foamed layer) are laminated. The non-foamed film (non-foamed layer)refers to a film structure that has not been subjected to a purposefulfoaming process (e.g. a process to incorporate foam cells), referring toa film essentially free of a foam cell structure. A typical example ofthe foam film is a resin film (e.g. a polyester-based resin film such asof PET) having an expansion rate of less than 1.1-fold (e.g. less than1.05-fold, typically less than 1.01-fold). When the substrate filmcomprises two or more foam layers, the materials and structures of thesefoam layers can be identical or different. When the foam film has amulti-layer structure that includes a foam layer, from the standpoint ofincreasing the tightness between layers, adhesive layers may be placedbetween the layers.

The foam film is not particularly limited in average foam cell diameter;it is usually suitably 10 μm to 200 μm, preferably 20 μm to 180 μm, ormore preferably 30 μm to 150 μm. When the average foam cell diameter is10 μm or larger, the impact-absorbing properties tend to increase. Onthe other hand, when the average foam cell diameter is 200 μm orsmaller, the handling properties and waterproof properties(water-blocking properties) tend to increase.

The average foam cell diameter (μm) of the foam film can be determined,using a low-vacuum scanning electron microscope to take an enlargedimage of a cross section of the foam and subjecting it to imageanalysis. About 20 to 30 foam cells can be analyzed. As the low-vacuumscanning electron microscope, for instance, product name S-3400NScanning Electron Microscope available from Hitachi High-Tech ScienceSystems Corporation) can be used.

The foam film is not particularly limited in density (apparent density);it is usually suitably 0.01 g/cm³ or higher, preferably 0.01 g/cm³ to0.7 g/cm³, or more preferably 0.02 g/cm³ to 0.5 g/cm³. When the densityis 0.01 g/cm³ or higher, the strength of the foam film (and even that ofthe PSA sheet) will increase with a tendency toward greater impactresistance and handling properties. On the other hand, when the densityis 0.7 g/cm³ or lower, the conformability to a difference in level tendsto increase without an excessive decrease in flexibility.

The density (apparent density) of the foam film is determined based onthe method described in JIS K 7222:1999. In particular, the foam film ispunched out into a 100 mm by 100 mm size to prepare a specimen and thedimensions of the specimen are measured. Using a 1/100 dial gauge with a20 mm diameter measurement terminal, the thickness of the specimen ismeasured. From these values, the volume of the foam film specimen isdetermined. The specimen is weighed on a top-loading balance (minimumscale 0.01 g or greater). From these values, the apparent density(g/cm³) of the foam film can be determined.

The 50% compressive stress of the foam film is not particularly limited.From the standpoint of the impact resistance, the foam film suitablyshows a 50% compressive stress of 0.1 N/cm² or greater. When the 50%compressive stress is at or above a certain value, for instance, even ifthe foam film is thin (e g about 100 μm thick), it can show sufficientresistance when compressed (resilience to compression) and maintain goodimpact resistance. The 50% compressive stress is preferably 0.2 N/cm² orgreater, or more preferably 0.5 N/cm² or greater. From the standpoint ofcombining flexibility and impact resistance in a well-balanced way, the50% compressive stress is suitably 8 N/cm² or less, preferably 6 N/cm²or less, or more preferably 3 N/cm² or less.

The 50% compressive stress (hardness) of the foam film is determinedbased on JIS K 6767:1999. In particular, the foam film is cut to 100 mmby 100 mm pieces. These pieces are layered to a total thickness of atleast 2 mm and the resultant is used as a measurement sample. At roomtemperature, using a compression tester, the measurement sample iscompressed at a rate of 10 mm/min. When compressed to 50% (whencompressed to 50% of its initial thickness) and held at 50% compressionfor 10 seconds, the value (resilience in N/cm²) is recorded as the 50%compressive stress. Other conditions (e.g. jig and calculation method,etc.) are conformed to JIS K 6767:1999.

The foam constituting the foam film disclosed herein is not particularlylimited in foam cell structure. The foam cell structure can be acontinuous foam cell structure, an isolated foam cell structure, or asemi-continuous foam cell structure. From the standpoint of the impactabsorbing properties, continuous and semi-continuous foam cellstructures are preferable.

The material of the foam film is not particularly limited. The foam filmcan be typically formed from a material comprising a polymer component(e.g. a thermoplastic polymer). A preferable foam film is usually formedof foam of a plastic material (plastic foam). The plastic material(which means to include a rubber material) for forming the plastic foamis not particularly limited; a suitable species can be selected amongknown plastic materials. For the plastic material (typically athermoplastic polymer), solely one species or a combination of two ormore species can be used. The primary component (typically a componentaccounting for more than 50% by weight) among the polymers in thesubstrate film or the foam film may be referred to as the “base polymer”hereinafter.

Specific examples of the foam include polyolefinic resin foam such as PEfoam and PP foam; polyester-based foam such as PET foam, polyethylenenaphthalate foam and polybutylene terephthalate foam; polyvinylchloride-based resin foam such as polyvinyl chloride foam; vinylacetate-based foam; acrylic resin foam; polyphenylene sulfide resinfoam; amide-based resin foam such as polyamide (nylon) resin foam andall-aromatic polyamide (aramide) resin foam; polyimide-based resin foam;polyether ether ketone (PEEK) foam; styrene-based resin foam such aspolystyrene foam; and urethane-based resin foam such as polyurethaneresin foam. As the foam, rubber-based resin foam such as polychloroprenerubber foam can be used as well.

In a preferable embodiment, acrylic resin foam (foam formed from acrylicresin) is used as the foam. Here, the acrylic resin foam refers to foamcomprising an acrylic polymer as the base polymer. The acrylic polymerin this description is as defined later. As the alkyl (meth)acrylateforming the acrylic polymer, one, two or more species can be preferablyused among alkyl (meth)acrylates having acyclic alkyl groups with 1 to20 (preferably 1 to 8, typically 1 to 4) carbon atoms. Preferableexamples of the alkyl (meth)acrylate include ethyl acrylate, n-butylacrylate and 2-ethylhexyl acrylate. The amount of the alkyl(meth)acrylate as the primary monomer is suitably 70% by weight or moreof all monomers in the acrylic polymer, or preferably 75% by weight ormore (e.g. 80% by weight or more). The amount of the alkyl(meth)acrylate is suitably 98% by weight or less of all the monomers, orpreferably 97% by weight or less (e.g. 96% by weight or less).

The secondary monomer co-polymerizable with the alkyl (meth)acrylate asthe primary monomer may be useful in introducing crosslinking points inthe acrylic polymer or in increasing the cohesive strength of theacrylic polymer. As the secondary monomer, one, two or more species offunctional group-containing monomers can be used among, for instance,carboxy group-containing monomers, hydroxy group-containing monomers,acid anhydride group-containing monomers, amide group-containingmonomers, amino group-containing monomers, cyano group-containingmonomers, monomers having nitrogen atom-containing rings and the like.The secondary monomer can also be a vinyl ester-based monomer such asvinyl acetate, an aromatic vinyl compound such as styrene, a sulfonategroup-containing monomer, a phosphate group-containing monomer and thelike. The amount of the secondary monomer is suitably 0.5% by weight ormore of all monomers in the acrylic polymer, or preferably 1% by weightor more. The amount of the secondary monomer is suitably 30% by weightor less of all the monomers, or preferably 10% by weight or less.

When the foam is formed with an emulsion-based resin composition by afoaming method where gases including air are mixed in mechanically suchas by stirring, it is preferable that the monomers forming the acrylicpolymer comprise a nitrogen atom-containing monomer as the secondarymonomer. This facilitates the formation of foam cells in the foamingprocess and may increase the viscosity of the composition when formingthe foam (typically when drying the resin composition), whereby the foamcells are readily kept in the foam body.

Examples of the nitrogen atom-containing monomer include cyanogroup-containing monomers such as acrylonitrile and methacrylonitrile;lactam ring-containing monomers such as N-vinyl-2-pyrolidone; amidegroup-containing monomers such as (meth)acrylamide,N-hydroxyethyl(meth)acrylamide, N-methylolacrylamide,N,N-dimethylacrylamide, N,N-diethylacrylamide and diacetone acrylamide.These can be used solely as one species or in a combination of two ormore species. Among them, cyano group-containing monomers such asacrylonitrile and lactam ring-containing monomers such asN-vinyl-2-pyrolidone are preferable.

The amount of the nitrogen atom-containing monomer is suitably 2% byweight or more of all monomers in the acrylic polymer, or preferably 3%by weight or more (e.g. 4% by weight or more). The amount of thenitrogen atom-containing monomer is suitably 30% by weight or less ofall the monomers, or preferably 25% by weight or less (e.g. 20% byweight or less).

The method for obtaining the acrylic polymer is not particularlylimited. Various polymerization methods known as procedures for thesynthesis of acrylic polymer can be suitably used, such as solutionpolymerization, emulsion polymerization, bulk polymerization, suspensionpolymerization, active energy ray polymerization (e.g. UVpolymerization). For instance, a desirable acrylic polymer can beobtained by dissolving or dispersing a monomer mixture in a suitablepolymerization solvent (toluene, ethyl acetate, water, etc.) andcarrying out polymerization using a polymerization initiator such as anazo-based polymerization initiator and a peroxide-based initiator. Inview of the ease of foaming and environmental aspects, it is preferableto use acrylic resin foam (emulsion-based acrylic resin foam) obtainedby emulsion polymerization.

From the standpoint of increasing the cohesive strength, the acrylicresin foam-forming composition preferably comprises a crosslinkingagent. The type of crosslinking agent is not particularly limited. Amongvarious crosslinking agents, one, two or more species can be suitablyselected and used. Favorable examples of the crosslinking agent includeisocyanate-based crosslinking agents, epoxy-based crosslinking agents,oxazoline-based crosslinking agents, carbodiimide-based crosslinkingagents, melamine-based crosslinking agents and metal oxide-basedcrosslinking agents. In particular, oxazoline-based crosslinking agentsare preferable. The amount of the crosslinking agent used is notparticularly limited. To 100 parts by weight of the acrylic polymer, itis suitably selected from a range of about 10 parts by weight or less(e.g. about 0.005 part to 10 parts by weight, preferably about 0.01 partto 5 parts by weight).

In another preferable embodiment, polyolefinic resin foam (resin foamformed from a polyolefin) is used as the foam. As the plastic materialforming the polyolefinic foam, various known or commonly-usedpolyolefinic resins can be used without particular limitations. Examplesinclude polyethylene such as low density polyethylene (LDPE), linear lowdensity polyethylene (LLDPE), high density polyethylene (HDPE) andmetallocene catalyst-based linear low density polyethylene;polypropylene; ethylene-propylene copolymer; and ethylene-vinyl acetatecopolymer. Among these polyolefinic resins, solely one species or acombination of two or more species can be used.

From the standpoint of the impact resistance, waterproof properties,etc., favorable examples of the foam film in the art disclosed hereininclude a polyethylene-based foam film essentially formed ofpolyethylene-based resin foam and a polypropylene-based foam filmessentially formed of polypropylene-based resin foam. Here, thepolyethylene-based resin refers to resin formed from ethylene as theprimary monomer (i.e. the primary component among the monomers) and mayinclude HDPE, LDPE and LLDPE as well as ethylene-propylene andethylene-vinyl acetate copolymers of which ethylene is copolymerized ata ratio above 50% by weight. Similarly, the polypropylene-based resinrefers to resin formed from propylene as the primary monomer. As thefoam film in the art disclosed herein, a polypropylene-based foam filmcan be preferably used.

The foaming method for the foam film is not particularly limited. Inaccordance with the purpose, ease of procedures, etc., chemicalprocedures, physical procedures and so on can be employed individuallyor in combination. From the standpoint of the contamination, etc.,physical foaming methods are preferable. Specific examples include afoaming method where a film-forming material is prepared to contain afoaming agent such as a low boiling compound (e.g. a hydrocarbon) andthermally expandable microspheres and foam cells are formed from thefoaming agent, a foaming method where gases such as air are mechanicallymixed in, a foaming method by solvent removal which takes advantage ofremoval of a solvent such as water, and a foaming method using asupercritical fluid. For instance, a method where an inert gas (e.g.carbon dioxide) is injected into the foam film-forming polymer underincreased pressure and the resultant is placed under reduced pressure toform a foam film By this method, the average foam cell diameter can beeasily controlled to be at or below a certain value and the foam filmcan be easily made to have a lower density.

The foam film is fabricated by employing a foaming method as describedabove. The formation of the foam film is not particularly limited. Forinstance, when employing a foaming method that mechanically admixesgases such as air, a resin composition (e.g. an emulsion-based resincomposition) containing foam can be subsequently applied over asubstrate or release paper, etc., and allowed to dry to obtain a foamfilm. From the standpoint of the foam stability, etc., the dryingpreferably includes a preliminary drying step at or above 50° C., butbelow 125° C. as well as a main drying step at 125° C. to 200° C.Alternatively, foam can be formed continuously into a film using acalender, extruder, conveyer belt casting and so forth; or a methodwhere a kneaded mixture of foam-forming materials is foamed and moldedin a batch process can be employed. In forming the foam film, a surfacelayer may be removed by slicing to adjust the film to obtain desirablethickness and foam characteristics.

The thermoplastic polymer (e.g. a polyolefinic polymer) that can beincluded in the foam film may comprise a thermoplastic elastomer thatexhibits properties of rubber at room temperature, but showsthermoplasticity at a high temperature. From the standpoint of theflexibility and conformability, one, two or more species can be usedamong thermoplastic elastomers, for instance, olefinic elastomers suchas ethylene-propylene copolymer, ethylene-propylene-diene copolymer,ethylene-vinyl acetate copolymer, polybutene, polyisobutylene, andchlorinated polyethylene; styrene-based elastomers such asstyrene-butadiene-styrene copolymer; thermoplastic polyester-basedelastomers; thermoplastic polyurethane-based elastomers; andthermoplastic acrylic elastomers. Among them, a thermoplastic elastomerhaving a glass transition temperature of room temperature or lower (e.g.20° C. or lower). The thermoplastic elastomer content in the foam filmis preferably about 10% to 90% by weight (e.g. 20% to 80% by weight) ofthe thermoplastic polymer in the foam film.

From the standpoint of the ease of mixing a foam-forming gas and thefoam stability, as the foaming agent, various surfactants can be used inthe foam film-forming material (e.g. an emulsion-based acrylic resincomposition), with examples including anionic surfactants, cationicsurfactants, nonionic surfactants and amphoteric surfactants.Hydrocarbon-based and fluorine-based surfactants can be used as well. Inparticular, from the standpoint of reducing the foam cell diameters andstabilizing the foam, anionic surfactants are preferable; ammonium saltsof fatty acids (typically ammonium salts of higher fatty acids) such asammonium stearate are more preferable. For the surfactant, solely onespecies or a combination of two or more species can be used. Thesurfactant content is preferably about 0.1 part to 10 parts by weight(e.g. 0.5 part to 8 parts by weight) to 100 parts by weight of the basepolymer of the foam film. The foaming agent in this description includesnot only an agent that shows foaming capabilities, but also a foam celldiameter-adjusting agent to reduce the foam diameters as well as a foamstabilizer such as a foam-adjusting agent.

When the foam film-forming material is an aqueous dispersion (e.g. anacrylic emulsion), it is preferable to use a silicone-based compound asthe foaming agent. By this, the recovery of thickness (the degree andspeed of recovery) after compression tends to improve. A preferablesilicone-based compound has 2000 or fewer siloxane bonds. Examples ofthe silicone-based compound include silicone oil, modified silicone oil,and silicone resin. In particular, dimethyl silicone oil and methylphenyl silicone oil are preferable. As the silicone-based compound, asilicone-modified polymer (e.g. a silicone-modified acrylic polymer, asilicone-modified urethane-based polymer, etc.) can be used as well.These can be used solely as one species or in a combination of two ormore species. The silicone compound content is preferably about 0.01part to 5 parts by weight (e.g. 0.05 part to 4 parts by weight,typically 0.1 part to 3 parts by weight) to 100 parts by weight of thebase polymer of the foam film.

From the standpoint of stabilizing the foam and increasing the ease offilm formation, the foam film-forming material (e.g. an emulsion-basedacrylic resin composition) may comprise a thickener. The thickener isnot particularly limited. Examples include acrylic acid-basedthickeners, urethane-based thickeners and polyvinyl alcohol-basedthickeners. In particular, polyacrylic acid-based thickeners andurethane-based thickeners are preferable. The thickener content ispreferably about 0.1 part to 10 parts by weight (e.g. 0.1 part to 5parts by weight) to 100 parts by weight of the base polymer of the foamfilm.

When a foam-containing substrate is used as the substrate film, the foamfilm preferably comprises a foam-nucleating agent such as a metalhydroxide (e.g. magnesium hydroxide). This tends to facilitate theadjustment of the average foam cell diameter in the foam film to obtaindesirable impact-absorbing properties, flexibility and so on. Thefoam-nucleating agent can be a metal oxide, composite oxide, metalcarbonate, metal sulfate, etc. The foam-nucleating agent content ispreferably about 0.5 part to 125 parts by weight (e.g. 1 part to 120parts by weight) to 100 parts by weight of the base polymer of the foamfilm.

When using a foam-containing substrate as the substrate film, from thestandpoint of inhibiting the foam from degassing while foam cells arebeing formed, the foam film preferably comprises a degassing inhibitorsuch as fatty acid amides. A more preferable fatty acid amide has abis-amide structure. The degassing inhibitor can be a metal salt of afatty acid as well. The degassing inhibitor content is preferably about0.5 part to 10 parts by weight (e.g. 0.7 part to 8 parts by weight,typically 1 part to 6 parts by weight) to 100 parts by weight of thebase polymer of the foam film.

The substrate film (e g a foam film) may comprise a softener so as toprovide desirable fluidity to the film-forming material thereby toimprove properties such as flexibility. With the inclusion of a softenerin the foam film, properties such as ease of stretching the film andexpansion ratio can be preferably adjusted. For example, one, two ormore species can be preferably used among hydrocarbon-based softenerssuch as liquid paraffin, paraffin wax, micro wax and polyethylene wax;ester-based softeners such as glyceryl stearate; and fatty acid-basedsofteners. The softener content is preferably 0.5 part to 50 parts byweight (e.g. 0.8 part to 40 parts by weight, typically 1 part to 30parts by weight) to 100 parts by weight of the base polymer of thesubstrate film (e.g. a foam film).

When emulsion-based acrylic resin foam is used, an arbitraryanticorrosive may be included to prevent corrosion of metal partsadjacent to the foam film. As the anticorrosive, an azolering-containing compound is preferable. With the use of an azolering-containing compound, inhibition of metal corrosion and tightadhesion to adherends can be combined at a high level. In particular, acompound with the azole ring forming a fused ring with an aromatic ringsuch as a benzene ring is preferable; benzotriazole-based compounds andbenzothiazole-based compounds are especially preferable. Theanticorrosive content is preferably about 0.2 part to 5 parts by weight(e.g. 0.3 part to 2 parts by weight) to 100 parts by weight of the basepolymer of the foam film.

In a preferable embodiment, the substrate film has transparency(including semi-transparency). In the PSA sheet comprising such asubstrate film, when bubbles and the like are trapped between the PSAsheet and an adherend, they are visible through the PSA sheet and arelikely to degrade the appearance. The art disclosed herein preventsformation of the sort of bubbles between the PSA sheet and the adherend;and therefore, an excellent appearance can be obtained in an embodimentcomprising a transparent substrate. In particular, the substrate filmmay show a total light transmittance of 80% or higher (e.g. 90% orhigher, typically 95% or higher). The substrate film preferably has ahaze value of 10% or lower (e.g. 5% or lower).

To obtain desirable designs and optical properties, the substrate film(e g a resin film) may be colored black, white or other with varioustypes of colorant (e.g. pigment) content. As a black colorant, carbonblack is preferable. It is also possible to employ a method where atleast one surface (one or each face) of the substrate film is subjectedto printing to overlay one, two or more colored layers (e.g. a blacklayer and a white layer).

To the substrate film (e g a resin substrate film, a foam substratefilm), various additives may be added as necessary, such as filler(inorganic filler, organic filler, etc.), anti-aging agent, antioxidant,UV ray absorber, antistatic agent, slip agent and plasticizer.

When the PSA sheet is adhesive on one face, between the two surfaces ofthe substrate film, the surface (back face) opposite from the surface tobe provided with a PSA layer is preferably made smooth. The smoothsurface may be the outer face of the PSA sheet; and therefore, when thePSA sheet having the smooth surface is used as, for instance, adecorative sheet or a surface protection sheet, it may provide a betterappearance (design). In a preferable embodiment, from the standpoint ofthe adhesive properties and the quality of appearance (design), the backface of the substrate film may have an arithmetic mean surface roughnessof 1 μm or less (e.g. about 0.05 μm to 0.75 μm, typically about 0.1 μmto 0.5 μm). In this description, the arithmetic mean surface roughnesscan be measured using a general surface roughness gauge (e.g.non-contact three-dimensional surface profilometer under model name WYKONT-3300 available from Veeco).

When an adhesively single-faced PSA sheet is wound to bring the backface of the substrate film in contact with the PSA layer surface, theback face (opposite from the surface to be provided with a PSA layer) ofthe substrate film may be subjected as necessary to release treatmentwith a silicone-based, long chain alkyl-based, fluorine-based releaseagent or the like. The release treatment brings about effects such aseasier unwinding of the PSA sheet wound in a roll. On the other hand,the PSA layer-side surface of the substrate film may be subjected to aheretofore known surface treatment such as corona discharge treatmentand primer coating for purposes such as increasing the tightness ofadhesion between the substrate and the PSA layer.

The thickness of the substrate film is not particularly limited and canbe suitably selected in accordance with the purpose. In general, thesubstrate thickness is suitably 1 μm or larger (e.g. about 2 μm to 500μm), or preferably about 5 μm to 500 μm (e.g. 10 μm to 200 μm, typically15 μm to 100 μm). In a preferable embodiment, the thickness of thesubstrate film is about 30 μm or smaller, more preferably 12 μm orsmaller, or yet more preferably smaller than 10 μm (e.g. smaller than 5μm, typically smaller than 3 μm). It is advantageous to limit thethickness of the substrate film in view of making the PSA sheet thinner,smaller, lighter, resources-saving, and so on.

When the substrate film comprises a foam film, the thickness of thefoam-containing substrate (e.g. a foam substrate film) can be suitablyselected in accordance with the strength and flexibility of the PSAsheet, intended purposes and so on. From the standpoint of theimpact-absorbing properties, etc., the foam-containing substrate has athickness of suitably 30 μm or larger, preferably 50 μm or larger, ormore preferably 60 μm or larger (e.g. 80 μm or larger). From thestandpoint of making the PSA sheet thinner, smaller, lighter,resource-saving, and so on, the thickness of the foam-containingsubstrate is usually suitably 1 mm or smaller. The use of the foam filmdisclosed herein can bring about excellent impact-absorbing capabilitieseven when the thickness is about 350 μm or smaller (more preferably 250μm or smaller, e.g. 180 μm or smaller). The thickness of the foam film(possibly a foam layer) in the foam-containing substrate can also bepreferably selected from the ranges exemplified as the thickness of theaforementioned foam-containing substrate.

<PSA Layer>

The PSA layer disclosed herein typically refers to a layer formed of amaterial (PSA) that exists as a soft solid (a viscoelastic material) ina room temperature range and has a property to adhere easily to adherendwith some pressure applied. As defined in “Adhesion Fundamental andPractice” by C. A. Dahlquist (McLaren & Sons (1966), P. 143), the PSAreferred to herein is generally a material that has a propertysatisfying complex tensile modulus E*(1 Hz)<10⁷ dyne/cm² (typically, amaterial that exhibits the described characteristics at 25° C.).

The PSA layer disclosed herein may comprise, as its base polymer, one,two or more species among acrylic polymers, rubber-based polymers,polyester-based polymers, urethane-based polymers, polyether-basedpolymers, silicone-based polymers, polyamide-based polymers,fluorine-based polymers, etc. From the standpoint of the adhesiveproperties (e.g. peel strength, repulsion resistance), molecular design,etc., acrylic polymers can be preferably used. In other words, the PSAlayer is preferably an acrylic PSA layer that comprises an acrylicpolymer as its base polymer. The “base polymer” of a PSA refers to theprimary component (typically, a component accounting for more than 50%by weight) among polymers in the PSA.

As the acrylic polymer, for example, a polymer of a monomeric startingmaterial comprising an alkyl (meth)acrylate as a primary monomer andpossibly comprising a secondary monomer copolymerizable with the primarymonomer is preferable. The primary monomer herein refers to a componentthat accounts for higher than 50% by weight of the monomer compositionin the monomeric starting material.

As the alkyl (meth)acrylate, for instance, a compound represented by thefollowing formula (1) can preferably be used:

CH₂═C(R¹)COOR²  (1)

Herein, R¹ in the formula (1) is a hydrogen atom or a methyl group. R²is a acyclic alkyl group having 1 to 20 carbon atoms (hereinafter, sucha numerical range of carbon atoms may be indicated as “C₁₋₂₀”). From thestandpoint of the storage elastic modulus of the PSA, etc., an alkyl(meth)acrylate having a C₁₋₁₂ (e.g. C₂₋₁₀, typically C₄₋₈) acyclic alkylgroup for R² is preferable. For the alkyl (meth)acrylate having a C₁₋₂₀acyclic alkyl group for R², solely one species or a combination of twoor more species can be used. Preferable alkyl (meth)acrylates includen-butyl acrylate and 2-ethylhexyl acrylate.

The secondary monomer copolymerizable with the alkyl (meth)acrylate asthe primary monomer may be useful in introducing crosslinking pointsinto the acrylic polymer and increasing the cohesive strength of theacrylic polymer. As the secondary monomer, one, two or more species canbe used among functional group-containing monomers such as carboxygroup-containing monomers, hydroxy group-containing monomers, acidanhydride group-containing monomers, amide group-containing monomers,amino group-containing monomers, and monomers having nitrogen-containingrings. The secondary monomer may also be a vinyl ester-based monomersuch as vinyl acetate, an aromatic vinyl compound such as styrene, asulfonate group-containing monomer, a phosphate group-containingmonomer, etc. For instance, from the standpoint of increasing thecohesive strength, an acrylic polymer in which a carboxygroup-containing monomer or a hydroxy group-containing monomer iscopolymerized as the secondary monomer is preferable. Preferableexamples of the carboxy group-containing monomer include acrylic acidand methacrylic acid. Preferable examples of the hydroxygroup-containing monomer include 2-hydroxyethyl acrylate and4-hydroxybutyl acrylate.

The amount of the secondary monomer is suitably 0.5% by weight of allmonomers in the acrylic polymer, or preferably 1% by weight or more. Theamount of the secondary monomer is suitably 30% by weight or less of allthe monomers, or preferably 10% by weight or less (e.g. 5% by weight orless). When a carboxy group-containing monomer is copolymerized in theacrylic polymer, from the standpoint of combining adhesive strength andcohesive strength, the carboxy group-containing monomer content ispreferably within a range of about 0.1% to 10% by weight (e.g. 0.2% to8% by weight, typically 0.5% to 5% by weight) of all the monomers usedin the synthesis of the acrylic polymer. When a hydroxy group-containingmonomer is copolymerized in the acrylic polymer, from the standpoint ofcombining adhesive strength and cohesive strength, the hydroxygroup-containing monomer content is preferably within a range of about0.001% to 10% by weight (e.g. 0.01% to 5%, typically 0.02% to 2% byweight) of all the monomers used in the synthesis of the acrylicpolymer. When a vinyl ester-based monomer such as vinyl acetate iscopolymerized as the secondary monomer, the vinyl ester-based monomercontent is preferably about 30% by weight or less (typically 0.01% to30% by weight, e.g. 0.1% to 10% by weight) of all the monomers used inthe synthesis of the acrylic polymer.

The method for obtaining the acrylic polymer is not particularlylimited. Various polymerization methods known as procedures for thesynthesis of acrylic polymer can be suitably employed, such as solutionpolymerization, emulsion polymerization, bulk polymerization andsuspension polymerization. It is also possible to employ active energyray radiation polymerization which involves irradiation of UV, etc. Forinstance, a desirable acrylic polymer can be obtained by dissolving ordispersing a monomer mixture in a suitable polymerization solvent(toluene, ethyl acetate, water, etc.) and carrying out polymerizationusing a polymerization initiator such as an azo-based polymerizationinitiator and a peroxide-based initiator.

From the standpoint of combining adhesive strength and cohesive strengthin a well-balanced way, the acrylic polymer disclosed herein preferablyhas a weight average molecular weight (Mw) in a range of 10×10⁴ orhigher, but 100×10⁴ or lower. An acrylic polymer whose Mw is 20×10⁴ orhigher, but 70×10⁴ or lower (e.g. 30×10⁴ or higher, but 50×10⁴ or lower)may bring about better results. In this description, Mw refers to thevalue based on standard polystyrene obtained by GPC (gas permeationchromatography).

From the standpoint of increasing the cohesive strength, the PSAcomposition preferably comprises a crosslinking agent. The type ofcrosslinking agent is not particularly limited; one, two or more speciescan be suitably selected and used among heretofore known crosslinkingagents. Preferable examples of the crosslinking agent includeisocyanate-based crosslinking agents and epoxy-based crosslinkingagents. The amount of the crosslinking agent used is not particularlylimited. For instance, to 100 parts by weight of the acrylic polymer, itcan be selected from a range of about 10 parts by weight or less (e.g.about 0.005 part to 10 parts by weight, preferably about 0.01 part to 5parts by weight).

The PSA layer disclosed herein may have a composition comprising atackifier. The tackifier is not particularly limited. Various tackifierresins can be used, such as rosin-based tackifier resin, terpene-basedtackifier resin, hydrocarbon-based tackifier resin, epoxy-basedtackifier resin, polyamide-based tackifier resin, elastomer-basedtackifier resin, phenolic tackifier resin, and ketone-based tackifierresin. These tackifier resins can be used solely as one species or in acombination of two or more species.

The tackifier resin preferably has a softening point (temperature ofsoftening) of about 60° C. or higher (preferably about 80° C. or higher,typically 100° C. or higher). By this, the PSA sheet can be obtainedwith higher adhesive strength. The upper limit of the softening point ofthe tackifier resin is not particularly limited; it can be about 180° C.or lower (e.g. about 140° C. or lower). The softening point of tackifierresin referred to herein is defined as the value measured by thesoftening point test method (ring and ball method) specified either inJIS K5902:2006 or in JIS K2207:2006.

The amount of tackifier resin can be suitably selected in accordancewith the target adhesive properties (adhesive strength, etc.). Forinstance, by solid content, it is preferable to use a tackifier at aratio of about 10 parts to 100 parts by weight (more preferably 20 partsto 80 parts by weight, or yet more preferably 30 parts to 60 parts byweight) relative to 100 parts by weight of the base polymer (preferablyan acrylic polymer).

The PSA composition may comprise, as necessary, various additivesgenerally known in the field of PSA compositions, such as levelingagent, crosslinking accelerator, plasticizer, softening agent, filler,anti-static agent, anti-aging agent, UV-absorbing agent, antioxidant andphoto-stabilizing agent. With respect to these various additives,heretofore known species can be used by typical methods.

The PSA layer disclosed herein may be formed from aqueous,solvent-based, hot-melt, and active energy ray-curable types of PSAcomposition, etc. The aqueous PSA composition refers to a PSAcomposition in a form comprising PSA (PSA layer-forming components) in asolvent whose primary component is water (in an aqueous solvent),typically including a so-called water-dispersed PSA composition (acomposition in a form where at least part of the PSA is dispersed inwater). The solvent-based PSA composition refers to a PSA composition ina form comprising PSA in an organic solvent. From the standpoint ofreducing environmental stress, an aqueous PSA composition is preferable.From the standpoint of the adhesive properties, etc., a solvent-basedPSA composition is preferably used.

The PSA layer disclosed herein can be formed by a heretofore knownmethod. For instance, a transfer method can be preferably used, in whicha PSA composition is provided to a releasable surface (a release face)and allowed to dry to form a PSA layer on the surface and the PSA layeris transferred to a substrate. Alternatively, a direct method can alsobe employed, in which a PSA composition is directly provided (typicallyapplied) to a substrate and allowed to dry to form a PSA layer. As therelease face, a release liner surface, the back face of a substratetreated with a release agent, and the like can be used.

The PSA composition can be applied using a known or commonly usedcoater, such as a gravure roll coater, reverse roll coater, kiss rollcoater, comma coater, dip roll coater, die coater, bar coater, knifecoater, and spray coater. Alternatively, the PSA composition can beapplied by immersion, curtain coating, etc.

From the standpoint of facilitating the crosslinking reaction,increasing the productivity, etc., the PSA composition is preferablyheated to dry. The drying temperature can be, for instance, about 40° C.to 150° C., or usually preferably about 60° C. to 130° C. After dried,the PSA composition can be further allowed to age for adjustment ofmigration of the components in the PSA layer, for the progress of thecrosslinking reaction, for releasing the distortion possibly present inthe substrate and PSA layer, etc.

The thickness of the PSA layer disclosed herein is not particularlylimited; it can be suitably selected in accordance with the purpose.Usually, from the standpoint of the productivity such as the dryingefficiency, adhesive properties, etc., it is suitably about 0.5 μm to200 μm, or preferably about 2 μm to 200 μm (e.g. 5 μm to 100 μm,typically 10 μm to 50 μm). In a preferable embodiment, the thickness ofthe PSA layer is 20 μm or smaller, more preferably 10 μm or smaller, oryet more preferably 7 μm or smaller (e.g. 5 μm or smaller). According tothe art disclosed herein, even in an embodiment where the PSA layer islimited in thickness as above, good air release properties can beobtained. It is advantageous to limit the thickness of the PSA layer inview of making the PSA sheet thinner, smaller, lighter, resource-saving,and so on. When the art disclosed herein is implemented in an embodimentof an adhesively double-faced sheet having a PSA layer on each face of asubstrate, the thicknesses of the respective PSA layers can be the sameor different.

<Coating Layer>

The coating layer partially covering the PSA layer surface is notparticularly limited as long as it can provide air release properties. Afavorable example of the coating layer material is a resin material.From the standpoint of the appearance, the coating layer is preferablyformed from a transparent or semi-transparent resin material.

Examples of the resin material form which the coating layer can beformed include a polyurethane-based resin, a phenolic resin, anepoxy-based resin, a polyamide-based resin, a urea melamine-based resin,a silicone-based resin, a polysilazane-based resin, a fluororesin, aphenoxy resin, a methacrylic resin, an acrylic resin, an acrylicurethane-based resin, an acrylic styrene-based resin, a polyarylateresin, a polyester-based resin, a polyolefinic resin, apolystyrene-based resin, polyvinyl chloride, a vinyl chloride/vinylacetate copolymer, polyvinyl acetate, polyvinylidene chloride,polycarbonate, a cellulose, and a polyacetal. The resin can be one, twoor more species of resin selected from various types of resins includinga heat-curable resin, a UV-curable resin, an electron beam-curableresin, and a two-component resin that is curable upon mixing.

The coating layer disclosed herein may comprise as necessary variousadditives such as fillers, anti-aging agent, antioxidant, UV absorber,crosslinking agent, slip agent, colorant (pigment, dye, etc.),antistatic agent, viscosity-adjusting agent (thixotropic agent,thickening agent, etc.), and film-forming aid.

The coating layer is typically non-adhesive or weakly adhesive. Thispreferably brings about good air release properties. Here, that thecoating layer is non-adhesive or weakly adhesive means that the coatinglayer has a 180° peel strength less than 3 N/25 mm (typically less than1 N/25 mm, including unmeasurably low adhesive strength). In particular,the 180° peel strength of the coating layer is determined by thefollowing method: The PSA sheet having a coating layer over the entirePSA layer surface is cut to a 25 mm wide by 100 mm long size to obtain ameasurement sample; in an environment at 23° C., 50% RH, the measurementsample is press-bonded over its coating layer surface to the surface ofa stainless steel plate (SUS304BA plate) with a 2 kg roller moved backand forth once. If it does not adhere, it is considered non-adhesivehere. The resultant is left standing in the same environment for 30minutes. Using a universal tensile/compression tester, based on JIS Z0237:2000, it is then measured for peel strength (N/20 mm) at a tensilespeed of 300 mm/min at a peel angle of 180°.

The method for placing the coating layer on the PSA layer surface is notparticularly limited. In typical, a method as described next isemployed. In particular, a coating layer-forming composition is preparedas necessary by dissolution or dispersion in a suitable solvent.Subsequently, by employing a suitable method among various known orcommonly-used printing methods, the composition is provided to areleasable surface of a releasable support (or a coatinglayer-transferring film, typically a release liner) and allowed to cure.The releasable support surface on which the coating layer is formed isbrought into contact with the PSA layer surface to transfer the coatinglayer onto the PSA layer surface. The coating layer is thus partiallyplaced on the PSA layer surface. For instance, a desirable coating layerpattern such as a lattice pattern can be preferably formed by employinga method such as offset printing, silk screen printing, letterpressprinting, flexographic printing, gravure printing, and inkjet printing.From the standpoint of the air release properties, gravure printing ismore preferable. Alternatively, the same embodiment can also be obtainedby forming a coating layer on a releasable surface as described aboveand further forming a PSA layer to cover the coating layer. In thiscase, the resulting PSA layer is subsequently transferred onto a surfaceof a substrate film. Based on technical common knowledge in thepertinent field, a skilled person can employ a method as describedabove, select a coating layer material in view of the wetting propertiesrelative to the releasable surface of the releasable support, adjust theviscosity of the coating layer-forming composition to a suitable range,and further select, for instance, a suitable printing means to form acoating layer having a cross-sectional shape disclosed herein.

The thickness of the coating layer can be designed to obtain desirableair release properties and is not particularly limited. From thestandpoint of the smoothness of the PSA sheet's adhesive face and thelamination on the PSA layer, it is preferable that the thickness of thecoating layer is about equal to or less than the thickness of the PSAlayer. In a preferable embodiment, the ratio (T_(C)/T_(A)) of thethickness T_(C) of the coating layer to the thickness T_(A) of the PSAlayer is 0.75 or less, more preferably 0.70 or less, or yet morepreferably 0.5 or less (e.g. 0.4 or less). For instance, a higher degreeof smoothness is obtained in an embodiment where the PSA layer has athickness of 1 μm or greater (preferably 2 μm or greater, or morepreferably 3 μm or greater) while satisfying the ratio (T_(C)/T_(A)). Inanother preferable embodiment, from the standpoint of combining airrelease properties and appearance, the thickness of the coating layer ispreferably up to about a half (e.g. up to one-third, typically up toone-fifth) the thickness of the PSA layer.

From the standpoint of the air release properties, productivity, etc.,the particular thickness of the coating layer is preferably 0.1 μm orgreater (e.g. 0.5 μm or greater, typically 1 μm or greater). From thestandpoint of the smoothness, the lamination and the appearance of theadhesive face of the PSA sheet, the coating layer has a thickness ofpreferably 10 μm or less, more preferably 5 μm or less, yet morepreferably 4 μm or less (e.g. less than 4 μm, typically 3 μm or less),or particularly preferably less than 3 μm (e.g. 2 μm or less). Accordingto the art disclosed herein, even when the coating layer is such a thinlayer, good air release properties are obtained. Such a thin coatinglayer is particularly preferable for use in applications that requirethinning (typically mobile electronic applications). The thickness ofthe coating layer can be obtained by SEM or TEM analysis of a crosssection of the PSA sheet.

<Release Liner>

The art disclosed herein is preferably implemented in an embodiment of arelease liner-backed PSA sheet that has a release liner protecting theadhesive face of the PSA sheet. As the release liner, any conventionalrelease paper or the like can be used without any particularlimitations. For example, a release liner having a release layer on asurface of a liner substrate such as resin film (PET, etc.) and paper; arelease liner formed from a poorly-adhesive material such as afluorine-based polymer (polytetrafluoroethylene, etc.) or apolyolefin-based resin (PE, PP, etc.); or the like can be used. Therelease layer can be formed, for instance, by subjecting the linersubstrate to a surface treatment with a release agent such as asilicone-based, a long-chain alkyl-based, a fluorine-based, a molybdenumdisulfide-based release agent or the like.

In a preferable embodiment, the release surface (on the side that makescontact with the PSA sheet's adhesive face) of the release liner(release film) is formed smooth. A good coating layer transfer can beobtained when a coating layer is partially formed on the releasablesurface of such a release liner and the release liner surface with thecoating layer partially formed thereon is brought into contact with aPSA layer to transfer the coating layer onto the PSA layer surface (inthis case, the release liner also serves as the coatinglayer-transferring film (release film)) The smooth texture of thesurface of the release liner is transferred onto the PSA layer surface,whereby the adhesive properties tend to increase as well. Similareffects can be obtained by partially forming a coating layer on thereleasable surface of such a release liner and further forming a PSAlayer on the releasable surface with the coating layer formed thereon soas to cover the coating layer. In this case, the PSA layer formed istransferred to a surface of a substrate film. For these reasons, it ispreferable that the release surface of the release liner has anarithmetic average surface roughness of 1 μm or less (e.g. about 0.05 μmto 0.75 μm, typically about 0.1 μm to 0.5 μm).

As shown in FIG. 8, the release liner used in fabricating the PSA sheetdisclosed herein may be a coating layer-bearing release liner 110 thatcomprises a releasable support 20 having a releasable surface 120A. Thereleasable support 120 may have a release layer at least on one face ofa liner substrate, or it can be a support formed from a low-adhesivematerial. The releasable surface 120A of the releasable support 120 isprovided with a coating layer 30 that can be transferred to a PSA sheet.In other words, the coating layer 30 is arranged on the releasablesurface 120A in a state that it can be separated by an adhesive strengthof PSA, etc. With the use of such release liner 110 having atransferable coating layer 30 on the surface, the PSA sheet disclosedherein is preferably fabricated. The features (shape, arrangement,relative position, size, pattern, etc.) of the coating layer provided tothe releasable surface of the releasable support are basically the sameas the features of the coating layer on the adhesive face of the PSAsheet described earlier. Thus, details are omitted. The linearlyextending parts of the coating layer provided to the release liner arealso basically as described earlier, except that the first face is onthe releasable surface side and the second face forms the outer surfaceon the releasable face. Thus, details are omitted.

The thickness (overall thickness) of the release liner is notparticularly limited. From the standpoint of the ease of removal,handling properties, strength, etc., it is preferably about 10 μm to 500μm (e.g. 15 μm to 100 μm).

As described above, in applying the PSA sheet disclosed herein to anadherend, the sort of bubble formation can be efficiently prevented atthe interface with the adherend. Thus, in either application methodbetween application by hand (manual application) and application with anautomated applicator or the like (automated application), the ease ofapplication will improve. For example, when applied by manualapplication, the degree of dependence on skills of individuals can bereduced, thereby bringing about advantages such as increases inefficiency and quality of the application and their stabilization. Whenapplied by automated application, failures during application such astrapping of bubbles and reapplication work can be reduced. Accordingly,either by manual application or by automated application, it is possibleto bring about increases in application efficiency and quality,stabilization of the quality and so on, thereby increasing theproductivity and quality of products made with the use of the PSA sheetas well. The art disclosed herein can bring about more uniformapplication; and therefore, it is particularly favorable as a PSA sheetthat is applied with an automated applicator.

Between the PSA sheet and the adherend, the sort of bubble formation mayoccur, not just during the application, but also after the applicationas the time passes. In typical, after the PSA sheet is applied, uponstorage and use in an environment at a relatively high temperature (e.g.35° C. or higher), etc., aforementioned bubbles and the like may formbetween the PSA sheet and the adherend, causing degradation of theappearance. For instance, such high temperature conditions are likely tobe reached in factories and outdoor in summer, inside electronics, etc.According to the art disclosed herein, even when used for applicationsexposed to such high temperature environments, the sort of bubbleformation can be prevented.

With the benefit of the features described above, the PSA sheetdisclosed herein can be preferably used for application to surfaces ofvarious articles. In a preferable embodiment, it can be used asdecorative sheets and surface protection sheets of various kinds, afixing sheet for printing plates of flexographic printing and the like,a light-blocking sheet, and so on. For instance, it is preferable as adecorative sheet (typically a paint-substitute sheet) applied to vehicleexteriors, house building materials, and so on. It is also preferablefor use inside electronics such as displays (typically TV displays) as acover sheet used to increase the smoothness of the outer face of achassis or to cover uneven places such as of screw holes in surfaces ofvarious parts. The use of such a cover sheet can decrease unevenness ofthe appearance of the adherend's outer surface and make the dimensionalprecision uniform. It can also be preferably used as an exterior sheetfor battery packs for which the appearance is important.

Even when made thin, with the PSA sheet disclosed herein, it is possibleto prevent degradation of appearance quality after its application whilemaintaining good adhesive properties. Thus, it can be preferably usedfor applications (e.g. for mobile electronics) where a thinner build anda lighter weight are required desirably with saving of resources. Inparticular, it can be preferably used as a surface protection sheet formobile electronics such as mobile phones, smartphones, tablet PCs,notebook PCs, various wearable devices (e.g. wrist wearables put onwrists such as wrist watches; modular devices attached to bodies withclips, straps, etc.; eye wears including eye glass types (monocular orbinocular, including head-mounted pieces); clothing types worn as, forinstance, accessories on shirts, socks, hats/caps, etc.; ear-mountedpieces put on ears such as earphones), digital cameras, digital videocameras, acoustic equipment (portable music players, IC recorders,etc.), calculators (e.g. pocket calculators), handheld game devices,electronic dictionaries, electronic notebooks, electronic books, vehiclenavigation devices, portable radios, portable TVs, portable printers,portable scanners, and portable modems; for bonding/fixing applicationsin liquid crystal displays of these mobile electronics; for fixingprotection panels (lenses) to protect the displays of these mobileelectronics; for fixing key modules of mobile phones; for fixing rimsheets, decorative panels, batteries, and various other parts; fixinglabels (including various marks) such as logos (letter logos) andvarious designs (symbols); and for like purposes. When used for themobile electronics, the PSA sheet may have a shape in accordance withthe purpose and so on, such as a frame shape and a ribbon shape (a stripshape). In this description, to be “mobile,” it is not sufficient thatit can be just carried, but it needs to be mobile enough for anindividual (an average adult) to be able to carry it by hand relativelyeasily.

Matters disclosed by this description include the following:

(1) A PSA sheet comprising a substrate film and a PSA layer provided toat least one face of the substrate film, wherein

the PSA sheet further comprises a coating layer that partially coversthe surface of the PSA layer,

the PSA sheet has an adhesive face formed of the PSA layer and thecoating layer,

the coating layer has a linearly extending part that runs from one edgeto another edge of the adhesive face,

the linearly extending part has a first face forming the adhesive faceof the PSA sheet and a second face located on the PSA layer siderelative to the first face, and

the second face of the linearly extending part forms an overall gentlycurved line in a cross section that perpendicularly intersects thelength direction of the linearly extending part.

(2) The PSA sheet according to (1) above, wherein, in the cross sectionthat perpendicularly intersects the length direction of the linearlyextending part, the second face of the linearly extending part has asegment that starts from one edge of the linearly extending part andruns towards the middle in a gently curved line in the depth directionof the PSA layer.(3) The PSA sheet according to (1) or (2) above, wherein, in the crosssection that perpendicularly intersects the length direction of thelinearly extending part, the second face of the linearly extending parthas an inclined segment that runs from one edge of the linearlyextending part in the depth direction of the PSA layer and a flatsegment that includes the deepest point of the linearly extending partand runs mostly parallel to the adhesive face.(4) The PSA sheet according to (3) above, wherein the inclined segmentis curved, convex on the PSA layer side.(5) The PSA sheet according to any one of (1) to (4) above, wherein thelinearly extending part has a thickness T and a width W with a W/T ratioof 50 or higher.(6) The PSA sheet according to any one of (1) to (5) above, wherein thelinearly extending part has a width of 100 μm or greater.(7) The PSA sheet according to any one of (1) to (6) above, wherein thePSA layer comprises an acrylic polymer that accounts for more than 50%(by weight) of all polymers in the PSA layer, with the acrylic polymercomprising, as a monomer, more than 50% (by weight) alkyl (meth)acrylaterepresented by a formula (1):

CH₂═C(R¹)COOR²  (1)

(in the formula (1), R¹ is a hydrogen atom or a methyl group; R² is anacyclic alkyl group with 1 to 20 carbon atoms).(8) The PSA sheet according to (7) above, wherein the alkyl(meth)acrylate is n-butyl acrylate and/or 2-ethylhexyl acrylate.(9) The PSA sheet according to (7) or (8) above, wherein the acrylicpolymer is an acrylic polymer in which a carboxy group-containingmonomer and/or a hydroxy group-containing monomer is copolymerized assecondary monomer(s).(10) The PSA sheet according to any one of (7) to (9) above, wherein theacrylic polymer is an acrylic polymer in which at least one species ofsecondary monomer selected from the group consisting of acrylic acid,methacrylic acid, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate iscopolymerized.(11) The PSA sheet according to any one of (7) to (10) above, wherein acarboxy group-containing monomer is copolymerized in the acrylicpolymer, the copolymerization ratio of the carboxy group-containingmonomer being 0.1% to 10% (by weight) to all the monomers used insynthesizing the acrylic polymer.(12) The PSA sheet according to any one of (7) to (11) above, wherein ahydroxy group-containing monomer is copolymerized in the acrylicpolymer, the copolymerization ratio of the hydroxy group-containingmonomer being 0.001% to 10% (by weight) to all the monomers used insynthesizing the acrylic polymer.(13) The PSA sheet according to any one of (7) to (12) above, whereinthe PSA layer comprises an isocyanate-based crosslinking agent and/or anepoxy-based crosslinking agent.(14) The PSA sheet according to any one of (7) to (13) above, whereinthe PSA layer comprises a tackifier resin with a softening point of 100°C. to 140° C. in an amount of 30 parts to 60 parts by weight to 100parts by weight of the acrylic polymer, the tackifier resin being atleast one species selected from the group consisting of a rosin-basedtackifier resin, a terpene-based tackifier resin and a hydrocarbon-basedtackifier resin.(15) The PSA sheet according to any one of (1) to (14) above, whereinthe coating layer comprises a transparent resin.(16) The PSA sheet according to any one of (1) to (15) above, whereinthe coating layer comprises at least one species of resins selected fromthe group consisting of a polyurethane-based resin, a phenolic resin, anepoxy-based resin, a polyamide-based resin, a urea melamine-based resin,a silicone-based resin, a polysilazane-based resin, a fluororesin, aphenoxy resin, a methacrylic resin, an acrylic resin, an acrylicurethane-based resin, an acrylic styrene-based resin, a polyarylateresin, a polyester-based resin, a polyolefinic resin, apolystyrene-based resin, polyvinyl chloride, a vinyl chloride/vinylacetate copolymer, polyvinyl acetate, polyvinylidene chloride,polycarbonate, a cellulose, and a polyacetal.(17) The PSA sheet according to any one of (1) to (16) above, whereinthe coating layer is of a polyurethane-based resin.(18) The PSA sheet according to any one of (1) to (17) above, whereinthe coating layer is of a two-component polyurethane-based resin that iscurable upon mixing.(19) The PSA sheet according to any one of (1) to (18) above, whereinthe substrate film is a polyolefinic resin film, a polyester-based resinfilm, a vinyl chloride-based resin film, a vinyl acetate-based resinfilm, a polyimide-based resin film, a polyamide-based resin film, afluororesin film, or a cellophane film.(20) The PSA sheet according to any one of (1) to (19) above, whereinthe substrate film is a polyester film.(21) The PSA sheet according to any one of (1) to (20) above, whereinthe substrate film is a polyethylene terephthalate film.(22) The PSA sheet according to any one of (1) to (21) above, whereinthe substrate film exhibits a total light transmittance of 80% orhigher.(23) The PSA sheet according to any one of (1) to (18) above, whereinthe substrate film is a foam film.(24) The PSA sheet according to (23) above, wherein the foam film has amean pore diameter of 10 μm to 200 μm and a density of 0.01 g/cm³ to 0.7g/cm³.(25) The PSA sheet according to (23) or (24) above, wherein the foamfilm is an acrylic resin foam body or a polyolefinic resin foam body.(26) The PSA sheet according to any one of (1) to (25) above, whereinthe coating layer has a thickness less than 3 μm.(27) The PSA sheet according to any one of (1) to (26) above for use inmobile electronics.(28) The PSA sheet according to any one of (1) to (27) above, whereinthe PSA layer has a thickness of 20 μm or less.(29) The PSA sheet according to any one of (1) to (28) above, whereinthe PSA layer has a thickness T_(A) and the coating layer has athickness T_(C) with a T_(C)/T_(A) ratio value of 0.75 or less.(30) The PSA sheet according to any one of (1) to (29) above,comprising, as the PSA layers, first and second PSA layers provided onfirst and second faces of the substrate film, respectively, wherein

the coating layer is partially placed on the surface of at least one PSAlayer between the first and second PSA layers.

(31) The PSA sheet according to any one of (1) to (30) above, whereinthe substrate film has a thickness less than 5 μm.(32) The PSA sheet according to any one of (1) to (31) above having anoverall thickness of 50 μm or less.(33) The PSA sheet according to any one of (1) to (32) above, whereinthe PSA layer surface has a coating layer-bearing area and a coatinglayer-free area, the coating layer-free area occupying 70% or more ofthe PSA layer surface.(34) The PSA sheet according to (33) above, wherein the linearlyextending part has a width in a range of 0.1 mm to 2 mm.(35) The PSA sheet according to (33) or (34) above, wherein

the PSA layer surface is provided with a plurality of the linearlyextending parts among which the linearly extending parts in a group areplaced at intervals arranged in the width direction, whereby the coatinglayer-bearing area has a stripe pattern.

(36) The PSA sheet according to (35) above, wherein the coatinglayer-bearing area comprises a first stripe pattern and a second stripepattern that is placed to intersect the first stripe pattern, wherebythe coating layer-bearing area has a lattice pattern.(37) The PSA sheet according to (35) or (36) above, wherein, in thecoating layer-bearing area, the intervals between the plurality of thelinearly extending parts forming one stripe pattern are in a range of1.0 mm to 10 mm.(38) The PSA sheet according to any one of (33) to (37) above having anadhesive face on which the coating layer is partially placed, theadhesive face exhibiting a 180° peel strength after 24-hour adhesion of13 N/25 mm or greater.(39) A release liner-backed PSA sheet comprising the PSA sheet accordingto any one of (1) to (38) above and a release liner that protects anadhesive face of the PSA sheet.(40) The release liner-backed PSA sheet according to (39) above,wherein, of the surfaces of the release liner, the adhesive face-sidesurface is formed smooth (wherein the release liner has a smooth surfaceon the adhesive face side).(41) A release liner for a PSA sheet, the release liner comprising areleasable support having at least one releasable face, wherein

the releasable face of the releasable support is provided with a coatinglayer disclosed herein that can be transferred onto a PSA sheet.

(42) The release liner according to (40) above, wherein the coatinglayer has a linearly extending part that runs from one edge to anotheredge of the releasable face,

the linearly extending part has a first face located on the releasableface side and a second face forming the outer surface on the releasableface, and

the second face of the linearly extending part forms an overall gentlycurved line in a cross section that perpendicularly intersects thelength direction of the linearly extending part.

(43) The release liner according to (41) or (42) above, wherein thecoating layer has a thickness less than 3 μm.(44) A method for producing the PSA sheet according to any one of (1) to(38) above, the method comprising:

a step of forming a PSA layer on a releasable face of a releasablesupport; and

a step of transferring the PSA layer onto a surface of a substrate film,the method being characterized by the following features:

a coating layer is partially formed on the releasable face of thereleasable support and the PSA layer-forming step is a step of furtherforming the PSA layer on the releasable face where the coating layer hasbeen formed; or no coating layer is formed on the releasable face of thereleasable support, the releasable support is removed from the PSA layerafter the PSA layer-transferring step, a coating layer-bearingreleasable support having a releasable face on which a coating layer ispartially formed is obtained, and the coating layer-bearing releasablesupport is layered over the PSA layer so that the coating layer istransferred onto the PSA layer surface.

(45) A method for producing the PSA sheet according to any one of (1) to(38) above, the method comprising:

a step of forming a coating layer partially on a releasable face of areleasable support;

a step of further forming a PSA layer on the releasable face where thecoating layer has been formed; and

a step of transferring the PSA layer onto a surface of a substrate film.

Several Examples related to the present invention are described below,but the present invention is not intended to be limited to theseExamples. In the description below, “parts” and “%” are by weight unlessotherwise noted.

Example (Preparation of PSA Composition)

In a reaction vessel equipped with a stirrer, thermometer, nitrogeninlet, reflux condenser and addition funnel, were placed 70 parts ofn-butyl acrylate, 30 parts of 2-ethylhexyl acrylate, 3 parts of acrylicacid, 0.05 part of 4-hydroxybutyl acrylate, 0.08 part ofazobisisobutyronitrile as polymerization initiator and toluene as thepolymerization solvent. Solution polymerization was carried out at 60°C. for 6 hours to obtain an acrylic polymer solution in toluene(viscosity 28 Pa·s, 40% non-volatiles). The resulting acrylic polymerhad a Mw of about 44×10⁴.

To 100 parts of the acrylic polymer in the toluene solution, was admixed30 parts of a polymerized rosin pentaerythritol ester (trade name PENSELD125 available from Arakawa Chemical Industries, Ltd.; softening point125° C.) followed by 3 parts of an isocyanate-based crosslinking agent(trade name CORONATE L available from Nippon Polyurethane Industry Co.,Ltd.) to prepare an acrylic PSA composition.

(Formation of Coating Layer)

A coating layer-forming material (urethane-based, two-component ink(curable when mixed)) was gravure-printed on the releasable face of 75μm thick release film (trade name FMN-75WD (C1-CA1) available fromFujiko Co., Ltd.) to form a coating layer (coating thickness about 1.5μm, transparent) in a lattice pattern. A coating layer-bearing releasefilm was thus obtained, with the coating layer formed partially on thereleasable face.

(Fabrication of PSA Sheets)

To the coating layer-bearing releasable face of the resulting coatinglayer-bearing release film, the PSA composition was applied and allowedto dry to a final thickness of 13 μm to obtain a PSA layer supported onthe release film. A 4 μm thick PET substrate film (trade name LUMIRRORavailable from Toray Industries, Inc.) was obtained. Onto the first face(corona discharge-treated face) of the PET substrate, the resulting PSAlayer was transferred along with the release film supporting it. Therelease film was used as it was to protect the PSA layer surface.

To the release agent-treated face of 38 μm thick release film (tradename DIAFOIL MRF-38 available from Mitsubishi Plastics, Inc.), the PSAcomposition was applied to a final thickness of 13 μm and allowed to dryat 100° C. for 3 minutes to obtain a PSA layer supported on the releasefilm. The resulting PSA layer was transferred along with the releasefilm supporting it onto the second face (corona discharge-treated face)of the PET substrate. The release film was used as it was to protect thePSA layer surface.

By transferring the respective PSA layers onto the two faces of the PETsubstrate by the methods described above, a substrate-supporteddouble-faced PSA sheet was fabricated, with the first face of the PETsubstrate provided with the coating layer-bearing PSA layer and thesecond face thereof provided with the coating layer-free PSA layer. Oneof the adhesive faces of the PSA sheet was a coating layer-bearingadhesive face where the coating layer in the lattice pattern shown inFIG. 1 was formed, with each coating layer band having a width (linewidth) of about 200 μm and the coating layer bands having a pitch ofabout 2 mm. The % surface area of the coating layer in the adhesive faceof the PSA sheet was 19%. FIGS. 1 to 12 show SEM cross-sectional imagesof the resulting PSA sheets. These cross-sectional images were takenfrom a cross section perpendicularly intersecting the length directionof a linearly extending part of the coating layer. The coating layer inthe images shows a band in the lattice pattern. The other adhesive faceof the PSA sheet was a coating layer-free adhesive face.

[Air Release Properties]

One face (the coating layer-free adhesive face) of the double-faced PSAsheet according to the present example was exposed, backed with 25 μmPET film, and cut to a 50 mm by 50 mm square to prepare a measurementsample. The coating layer-bearing adhesive face of the measurementsample was exposed and the measurement sample was placed (notpress-bonded) on a horizontally laid stainless steel plate (SUS plate)as the adherend, with the coating layer-bearing adhesive face being onthe adherend side.

A bubble-forming rubber plate was then obtained, laid and pressed overthe measurement sample to form bubbles between the adhesive face (thecoating layer-bearing adhesive face) of the measurement sample and theadherend surface. In particular, as the bubble-forming rubber plate, wasobtained a 50 mm by 50 mm square rubber plate having a 20 mm by 20 mmsquare opening (through hole) in the center of its face. Thebubble-forming rubber plate was laid over the top face (the backed face)of the measurement sample and pressed from the top at 3 kgf for 5seconds to press-bond the measurement sample's adhesive face (thecoating layer-bearing adhesive face) and the adherend surface over thearea corresponding to the frame shape of the rubber plate thereby toform bubbles between the measurement sample's adhesive face (the coatinglayer-bearing adhesive face) and the adherend surface over thenon-loaded area (20 mm by 20 mm square area) corresponding to theopening of the rubber plate.

The bubble-forming rubber plate was removed from the backed face of themeasurement sample. A 50 mm by 50 mm square rubber plate (with noopening) was laid over the backed face of the measurement sample andpressed from the top at 3 kgf for 15 seconds. The rubber plate wasremoved and the degree of elimination of the pre-formed bubbles wasvisually inspected. As the rubber plate, was used trade name NEO-200 (3mm thick) available from Irumagawa Rubber Co., Ltd. As thebubble-forming rubber plate, the same type of rubber plate was processedand used.

As a result of visual inspection, no leftover bubbles were found on theadhesive face (coating layer-bearing adhesive face) of the PSA sheet,confirming the good air release properties of the PSA sheet according tothe present example.

[Effective Adhesive Strength (Surface Condition of Adhesive Face)]

One face (the coating layer-free adhesive face) of the double-faced PSAsheet according to the present example was exposed, backed with 50 μmthick PET film, and cut to a 20 mm by 100 mm size to prepare ameasurement sample. Of the measurement sample, the coating layer-bearingadhesive face was exposed. In an environment at 23° C., 50% RH, theexposed adhesive face of the measurement sample was press-bonded to thesurface of a stainless steel plate (SUS plate) with a 5 kg roller movedback and forth once. The resultant was left standing in the sameenvironment for 24 hours. Subsequently, using a universaltensile/compression tester, based on JIS Z 0237:2000, the peel strength(N/20 mm) (24-hour adhesion strength) was determined at a tensile speedof 300 mm/min at a peel angle of 180°.

Without forming a coating layer, but otherwise in the same manner as thepresent example, a PSA sheet (coating layer-free PSA sheet) wasfabricated. In the same manner as described above, the resulting PSAsheet was adhered to the adherend and the 24-hour peel strength P_(C)(N/20 mm) was determined.

With the peel strength P_(C) of the coating layer-free PSA sheet (with100% PSA layer and 0% coating layer in the surface area of the adhesiveface) being 100%, the % surface area of the coating layer in theadhesive face of the PSA sheet according to the present example wassubtracted to determine the theoretical peel strength P_(T) (N/20 mm) ofthe PSA sheet according to the present example. In the present example,the % surface area of the coating layer in the adhesive face (coatinglayer-bearing adhesive face) of the PSA sheet was 19%; from100%−19%=81%, P_(T)=P_(C)×0.81. When the actual measured value P_(M)(the peel strength of the PSA sheet according to the present examplemeasured under the conditions described above) is 90% or more of thetheoretical peel strength P_(T) (i.e. when P_(M)≧P_(T)×0.9), it can bejudged that the coating layer formed on the PSA layer surface fit wellin the PSA layer, and the PSA sheet's adhesive face (coatinglayer-bearing adhesive face) had a good surface condition to achieve anear-theoretical value.

The PSA sheet according to the present example was tested as describedabove. As a result, the actual measured peel strength value P_(M) was atleast 90% of the theoretical peel strength P_(T).

[Tolerance for Thickness]

With the PSA sheet obtained according to the present example, using adial gauge, at 10 points of intersection in the coating layer latticeand 10 center points of rectangular areas with the exposed PSA layersurrounded by the coating layer in the lattice pattern, the thicknesswas measured. The maximum value T_(M) (μm) and the standard thicknessT_(S) (μm) of the thickness values were substituted into a formula(T_(M)−T_(S))/T_(S)×100 and the resulting value was used as thetolerance (%) for thickness. With the tolerance for thickness of the PSAsheet according to the present example being 50% or less, a Pass levelgrade can be given.

The PSA sheet according to the present example showed good air releaseproperties. It is presumed that the coating layer formed partially onthe PSA layer surface worked sufficiently as the air releasing means. Asshown in FIGS. 9 to 12, in the PSA sheet according to the presentexample, a linearly extending part (a band in the lattice pattern) had acertain cross-sectional shape. In particular, the second face located onthe PSA layer side of the linearly extending part formed an overallgently curved line in the cross section perpendicularly intersecting thelength direction of the linearly extending part. From the test results,the PSA sheet with the coating layer having the cross-sectional shapehad a good surface condition on the adhesive face, showed a smalltolerance for thickness, and had high quality

These results indicate that when the coating layer has a specificcross-sectional shape, good air release properties are obtained andhigher quality is achieved.

Although specific embodiments of the present invention have beendescribed in detail above, these are merely for illustrations and do notlimit the scope of claims. The art according to the claims includesvarious modifications and changes made to the specific embodimentsillustrated above.

REFERENCE SIGNS LIST

-   1, 2 PSA sheets-   1A adhesive face-   10 substrate film-   20, 21, 22 PSA layers-   20A PSA layer surface-   30 coating layer-   40 coating layer pattern (lattice pattern)-   42 first stripe pattern-   44 second stripe pattern-   50 linearly extending part (band)-   52 first face-   54 second face-   56 one edge (left edge) of the width direction of a linearly    extending part-   58 other edge (right edge) of the width direction of a linearly    extending part-   60 inclined segment-   62 flat segment-   70 coating layer-bearing area-   72 coating layer-free area-   100, 101, 102 release liners-   110 coating layer-bearing release liner-   120 releasable support-   120A releasable face

1. A pressure-sensitive adhesive sheet comprising a substrate film and apressure-sensitive adhesive layer provided to at least one face of thesubstrate film, wherein the pressure-sensitive adhesive sheet furthercomprises a coating layer that partially covers the surface of thepressure-sensitive adhesive layer, the pressure-sensitive adhesive sheethas an adhesive face formed of the pressure-sensitive adhesive layer andthe coating layer, the coating layer has a linearly extending part thatruns from one edge to another edge of the adhesive face, the linearlyextending part has a first face forming the adhesive face of thepressure-sensitive adhesive sheet and a second face located on thepressure-sensitive adhesive layer side relative to the first face, andthe second face of the linearly extending part forms an overall gentlycurved line in a cross section that perpendicularly intersects thelength direction of the linearly extending part.
 2. Thepressure-sensitive adhesive sheet according to claim 1, wherein, in thecross section that perpendicularly intersects the length direction ofthe linearly extending part, the second face of the linearly extendingpart has a segment that starts from one edge of the linearly extendingpart and runs towards the middle in a gently curved line in the depthdirection of the pressure-sensitive adhesive layer.
 3. Thepressure-sensitive adhesive sheet according to claim 1, wherein, in thecross section that perpendicularly intersects the length direction ofthe linearly extending part, the second face of the linearly extendingpart has an inclined segment that runs from one edge of the linearlyextending part in the depth direction of the pressure-sensitive adhesivelayer and a flat segment that includes the deepest point of the linearlyextending part and runs mostly parallel to the adhesive face.
 4. Thepressure-sensitive adhesive sheet according to claim 3, wherein theinclined segment is curved, convex on the pressure-sensitive adhesivelayer side.
 5. The pressure-sensitive adhesive sheet according to claim1, wherein the linearly extending part has a thickness T and a width Wwith a W/T ratio of 50 or higher.
 6. The pressure-sensitive adhesivesheet according to claim 1, wherein the linearly extending part has awidth of 100 μm or greater.
 7. The pressure-sensitive adhesive sheetaccording to claim 1, wherein the pressure-sensitive adhesive layercomprises an acrylic polymer that accounts for more than 50% by weightof all polymers in the pressure-sensitive adhesive layer, with theacrylic polymer comprising, as a monomer, more than 50% by weight alkyl(meth)acrylate represented by a formula (1):CH₂═C(R¹)COOR²  (1) wherein R¹ is a hydrogen atom or a methyl group; R²is an acyclic alkyl group with 1 to 20 carbon atoms. 8-11. (canceled)12. The pressure-sensitive adhesive sheet according to claim 7, whereina hydroxy group-containing monomer is copolymerized in the acrylicpolymer, the copolymerization ratio of the hydroxy group-containingmonomer being 0.001% to 10% by weight to all monomers used in thesynthesis of the acrylic polymer.
 13. The pressure-sensitive adhesivesheet according to claim 7, wherein the pressure-sensitive adhesivelayer comprises an isocyanate-based crosslinking agent and/or anepoxy-based crosslinking agent.
 14. The pressure-sensitive adhesivesheet according to claim 7, wherein the pressure-sensitive adhesivelayer comprises a tackifier resin with a softening point of 100° C. to140° C. in an amount of 30 parts to 60 parts by weight to 100 parts byweight of the acrylic polymer, and the tackifier resin is at least onespecies selected from the group consisting of a rosin-based tackifierresin, a terpene-based tackifier resin and a hydrocarbon-based tackifierresin.
 15. The pressure-sensitive adhesive sheet according to claim 1,wherein the coating layer comprises a transparent resin.
 16. (canceled)17. The pressure-sensitive adhesive sheet according to claim 1, whereinthe coating layer comprises a polyurethane-based resin.
 18. Thepressure-sensitive adhesive sheet according to claim 1, wherein thecoating layer is of a two-component part polyurethane-based resin thatis curable upon mixing.
 19. (canceled)
 20. The pressure-sensitiveadhesive sheet according to claim 1, wherein the substrate film is apolyester film. 21-22. (canceled)
 23. The pressure-sensitive adhesivesheet according to claim 1, wherein the substrate film is a foam film.24. The pressure-sensitive adhesive sheet according to claim 23, whereinthe foam film has a mean pore diameter of 10 μm to 200 μm and a densityof 0.01 g/cm³ to 0.7 g/cm³.
 25. The pressure-sensitive adhesive sheetaccording to claim 23, wherein the foam film is an acrylic resin foam ora polyolefinic resin foam. 26-38. (canceled)
 39. A release liner-backedpressure-sensitive adhesive sheet comprising the pressure-sensitiveadhesive sheet according to claim 1 and a release liner that protectsthe adhesive face of the pressure-sensitive adhesive sheet.
 40. Therelease liner-backed pressure-sensitive adhesive sheet according toclaim 39, wherein the release liner has a smooth surface on the adhesiveface side.
 41. A release liner for a pressure-sensitive adhesive sheet,the release liner comprising a releasable support having at least onereleasable face, wherein the releasable face of the releasable supportis provided with a coating layer capable of being transferred onto thepressure-sensitive adhesive sheet, the coating layer has a linearlyextending part that runs from one edge to another edge of the releasableface, the linearly extending part has a first face located on thereleasable face side and a second face forming the outer surface on thereleasable face, and the second face of the linearly extending partforms an overall gently curved line in a cross section thatperpendicularly intersects the length direction of the linearlyextending part. 42-44. (canceled)